Submit button won't work in PHP [Addresbook] : 
<!-- begin snippet: js hide: false -->

<!-- language: lang-html -->

    <?php
    if (!isset($_SESSION)) { session_start(); }




    include "connect.php";
    include "functions.php";
    if (!isset($_SESSION['login']) || $_SESSION['login'] !== true) {
    	header('location: no_acces.php');
    	exit();
    } else {
    	$id_user = $_SESSION['userid'];
    	$q_user = mysqli_query($conn, "SELECT * FROM users WHERE id = $id_user");
    	if (mysqli_num_rows($q_user) === 1) {
    		$r_user = mysqli_fetch_assoc($q_user);
    	} else {
    		unset($_SESSION['login']);
    		unset($_SESSION['userid']);
    		header('location: no_acces.php');
    		exit();
    	}
    }

    $error = "";

    $userQuery = mysqli_query($conn, "SELECT username FROM users");

    $user = mysqli_fetch_assoc($userQuery);
    $id = $_GET['id'];
    if (isset($_POST['edit_contact'])) {
        $roepnaam = $_POST['roepnaam'];
        $naam = $_POST['naam'];
        $land = $_POST['land'];
        $bedrijf = $_POST['bedrijf'];
        $adres1 = $_POST['adres1'];
        $adres2 = $_POST['adres2'];
        $stad = $_POST['stad'];
        $postcode = $_POST['postcode'];
        $provincie = $_POST['provincie'];
        $telefoon = $_POST['telefoon'];
        $email = $_POST['email'];
    		$captcha=	$_POST['g-recaptcha-response'];

        if(!$captcha){
                $error = "Er is een fout opgetreden";

              }


              if ($error == "") {
            		$insertUser = ("UPDATE address SET
            		roepnaam = '$roepnaam', naam = '$naam', bedrijf = '$bedrijf', telefoon = '$telefoon', email = '$email', adres1 = '$adres1', adres2 = '$adres2', stad = '$stad', postcode = '$postcode', provincie = '$provincie', land = '$land' WHERE id = $id");


            		if (mysqli_query($conn, $insertUser)) {
            			$_SESSION['edit_contact'] = true;
            			header('location: address_book.php');
            		} else {
            			$error = "Er is een fout opgetreden";
            		}
            	}
              }

     ?>




     <!DOCTYPE html>
     <html lang="en">
       <head>
       <link rel="stylesheet" href="bootstrap/css/bootstrap.min.css" type="text/css">
       <link rel="stylesheet" href="css/stylesheet.css" type="text/css">
       <script src="https://ajax.googleapis.com/ajax/libs/jquery/1.12.0/jquery.min.js"></script>
       <script src="http://maxcdn.bootstrapcdn.com/bootstrap/3.3.6/js/bootstrap.min.js"></script>
     	<script src='https://www.google.com/recaptcha/api.js'></script>
       <script src="js/java.js"></script>
         <meta charset="utf-8">
         <meta name="viewport" content="width=device-width, initial-scale=1">
         <title>Contact wijzigen</title>
       <style>
       .error {
     	color: darkred;
     	font-weight: bold;
       }
       </style>
       </head>
       <body>
         <nav class="navbar navbar-default">
         <div class="container-fluid">
           <div class="navbar-header">
             <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#myNavbar">
               <span class="icon-bar"></span>
               <span class="icon-bar"></span>
               <span class="icon-bar"></span>
             </button>
             <a class="navbar-brand" href="index.php">SBRM National Bank</a>
           </div>
           <div class="collapse navbar-collapse" id="myNavbar">
             <ul class="nav navbar-nav">
               <li><a href="index.php">Home</a></li>
               <li><a href="details.php">Gegevens</a><li>
               <li><a href="bankaccounts.php">Rekeningoverzicht</a><li>
               <li class="active"><a href="address_book.php">Contacten</a><li>

             </ul>
             <ul class="nav navbar-nav navbar-right">
               <li class-"active"><a href="details.php"><span class="glyphicon glyphicon-user"></span>  U bent ingelogd als <?php echo $user['username']; ?></a></li>
               <li><a href="logout.php"><span class="glyphicon glyphicon-log-out"></span> Uitloggen</a></li>
             </ul>
           </div>
         </div>
         </nav>
         <div class="container-fluid hero-slide">
           <div class="row">
         <div id="myCarousel" class="carousel slide " data-ride="carousel">



           <div class="carousel-inner" role="listbox">
             <div class="item active">
               <img src="images/tempc.jpg" alt="Ad">
         <div class="carousel-caption">
               <h3 class="caption">Contact wijzigen</h3>

             </div>
           </div>
           </div>
         </div>
         </div>
       </div>

     <div class="container padding-top-10">
       <div class="panel col-md-6">
         <div class="panel-heading "><h5>Nieuwe gegevens:</h5></div>
         <div class="panel-body">
           <form action="" method="post">
     	    <?php if ($error !== "") { ?>
     		<div class="row">
               <div class="col-md-12 error">
                 <?php echo $error; ?>
               </div>
             </div>
     		<?php } ?>
             <label for="firstName" class="control-label">Naam:</label>
             <div class="row ">
               <div class="col-md-6">
               <input type="text" class="form-control" id="firstName" placeholder="Roepnaam" name="roepnaam" value="<?php if (isset($_POST['roepnaam'])) { echo $_POST['roepnaam']; } ?>" required/>
             </div>
             <div class="col-md-6">
             <input type="text" class="form-control" id="lastName" placeholder="Naam" name="naam" value="<?php if (isset($_POST['naam'])) { echo $_POST['naam']; } ?>" required/>
           </div>
             </div>
     <label for="username" class="control-label">Bedrijf:</label>
             <div class="row ">
               <div class="col-md-12">
                 <input type="text" class="form-control" id="username" placeholder="Bedrijf" name="bedrijf" value="<?php if (isset($_POST['bedrijf'])) { echo $_POST['bedrijf']; } ?>" required/>
               </div>
             </div>
             <label for="password" class="control-label">Telefoonnummer:</label>
                     <div class="row ">
                       <div class="col-md-12">
                         <input type="text" class="form-control" id="password" placeholder="Telefoonnummer" name="telefoon" value="<?php if (isset($_POST['telefoon'])) { echo $_POST['telefoon']; } ?>" required/>
                       </div>

                     </div>
                     <label for="email" class="control-label">Email:</label>
                             <div class="row ">
                               <div class="col-md-12">
                                 <input type="text" class="form-control" id="email" placeholder="E-mailadres" name="email" value="<?php if (isset($_POST['email'])) { echo $_POST['email']; } ?>" required/>
                               </div>

                             </div>
     <label for="adres1" class="control-label">Adres:</label>
             <div class="row">
               <div class="col-md-12">
               <input type="text" class="form-control" id="adres1" placeholder="Adres 1" name="adres1" value="<?php if (isset($_POST['adres1'])) { echo $_POST['adres1']; } ?>" required/>
             </div>
             </div>
             <div class="row padding-top-10">
               <div class="col-md-12">
               <input type="text" class="form-control" id="adres2" placeholder="Adres 2" name="adres2" value="<?php if (isset($_POST['adres2'])) { echo $_POST['adres2']; } ?>"/>
             </div>
             </div>
             <div class="row">
               <div class="col-md-3">
                 <label for="postcode" class="control-label">Postcode:</label>
               </div>
               <div class="col-md-5">
                 <label for="city" class="control-label">Stad:</label>
               </div>
               <div class="col-md-4">
                 <label for="regio" class="control-label">Regio:</label>
               </div>
             </div>
             <div class="row ">
               <div class="col-md-3">
                 <input type="text" class="form-control" id="postcode" placeholder="Postcode" name="postcode" value="<?php if (isset($_POST['postcode'])) { echo $_POST['postcode']; } ?>" required/>
               </div>
               <div class="col-md-5">
                 <input type="text" class="form-control" id="city" placeholder="Stad" name="stad" value="<?php if (isset($_POST['stad'])) { echo $_POST['stad']; } ?>" required/>
               </div>
               <div class="col-md-4">
                 <input type="text" class="form-control" id="regio" placeholder="Provincie" name="provincie" value="<?php if (isset($_POST['provincie'])) { echo $_POST['provincie']; } ?>" required/>
               </div>
             </div>
             <label for="land" class="control-label">Land:</label>
                     <div class="row ">
                       <div class="col-md-12">
                         <input type="text" class="form-control" id="password" placeholder="Land" name="land" value="<?php if (isset($_POST['land'])) { echo $_POST['land']; } ?>" required/>
                       </div>

                     </div>

     								<div class="row">
     									<div class="col-md-8 padding-top-10 ">
     										<div class="g-recaptcha " data-sitekey="6LcCsBoTAAAAAK72uzyJSrgWwD8xuF6jFIfgFaHX"></div>
     									</div>
     								</div>
             <div class="row">
               <div class="col-md-2 padding-top-10">
                 <input type="submit" name="edit_contact" class="btn btn-succes" value="Wijzigen">
               </div>
    					 <div class="col-md-2 padding-top-10">
    						 <input type="text" name="delete_contact" action="delete_contact.php" class="btn btn-succes" value="Contact verwijderen">
    					 </div>
             </div>


           </form>
         </div>
     </div>
     </div>
     <footer>
       <div class="container">
         <div class="row">
           <div class="col-sm-3">
             <h6>Copyright &copy; 2016</h6>
             <ul class="list-unstyled">
               <li class="boss">Sander Bakker</li>
               <li class="unstyled">Bob Lansbergen</li>
               <li class="unstyled">Ronald van den Heuvel</li>
               <li class="unstyled">Max Donck</li>
             </ul>
           </div>
           <div class="col-sm-3">
             <h6>Over Ons</h6>
             <p id="pfont">Dit is een website ontworpen om een banksysteem te simuleren met PHP en mySQL</p>
           </div>

           <div class="col-sm-2">
             <h6>Navigatie</h6>
             <ul class="list-unstyled">
               <li class="unstyled"><a href="#">Home</a></li>
               <li class="unstyled"><a href="#">Particulier</a></li>
               <li class="unstyled"><a href="#">Persoonlijk</a></li>
               <li class="unstyled"><a href="#">Privé</a></li>
               <li class="unstyled"><a href="#">Zakelijk</a></li>
             </uL>
           </div>
           <div class="col-sm-2">
             <h6>Contact</h6>
             <ul class="list-unstyled">
               <li class="unstyled"><a href="#">Google +</a></li>
               <li class="unstyled"><a href="#">Facebook</a></li>
               <li class="unstyled"><a href="#">Twitter</a></li>
               <li class="unstyled"><a href="#">YouTube</a></li>
             </uL>
           </div>
         </div>
       </div>
     </footer>
       </body>
       </head>
       </html>


<!-- end snippet -->

This is my html code 

<!-- begin snippet: js hide: false -->

<!-- language: lang-html -->

    <?php
    if (!isset($_SESSION)) { session_start(); }


    include "connect.php";
    include "functions.php";
    if (!isset($_SESSION['login']) || $_SESSION['login'] !== true || !isset($_SESSION['userid']) || $_SESSION['userid'] == "") {
    	header('location: login.php');
    	exit();

    } else {
    	session_regenerate_id();
    }
    $id = $_GET['id'];

    $query = "DELETE FROM address WHERE id= $id";

    mysqli_query ($query);

    if (mysql_affected_rows() == 1) {
    header('location: addressbook.php');

    } else {
    echo "Verwijderen mislukt"; 

    }


    ?>


<!-- end snippet -->

This is my PHP code. 

I'm trying to make a delete button for my contacts within the addressbook. but everytime I click "Contact verwijderen" the webpage resets it self and the contact won't be deleted. Could anyone help me to fix this?