Redirect naar bedankingspagina werkt niet

<?php 
	if($_POST) {

		$to = "[email protected]"; // Your email here
		$subject = 'Bericht verstuurd van mijn site'; // Subject message here

	}

    //Send mail function
	function send_mail($to,$subject,$message,$headers){
		if(@mail($to,$subject,$message,$headers)){
			header('Location: http://www.mijnsite.be/bedankt.html');
			exit();
		} else {
			echo json_encode(array('info' => 'error', 'msg' => "Uw bericht is niet verzonden. Er is iets verkeerd gegaan. Probeer het nog eens."));
		}
	}	

	//Check e-mail validation
	function check_email($email){
		if(!preg_match("/^[_.\da-z-]+@[a-z\d][a-z\d-]+\.+[a-z]{2,6}$/i", $email)) {
			return false;
		} else {
			return true;
		}
	}

	//Get post data
	if(isset($_POST['name']) and isset($_POST['mail']) and isset($_POST['onderwerp']) and isset($_POST['comment'])){
		$name 	 = $_POST['name'];
		$mail 	 = $_POST['mail'];
		$onderwerp 	 = $_POST['onderwerp'];
		$website  = $_POST['website'];
		$comment = $_POST['comment'];

		if($name == '') {
			echo json_encode(array('info' => 'error', 'msg' => "Gelieve uw naam in te vullen."));
			exit();
		} else if($mail == '' or check_email($mail) == false){
			echo json_encode(array('info' => 'error', 'msg' => "Gelieve een geldig emailadres in te vullen."));
			exit();
		} else if($onderwerp == ''){
			echo json_encode(array('info' => 'error', 'msg' => "Gelieve uw onderwerp in te vullen."));
			exit();
		} else if($comment == ''){
			echo json_encode(array('info' => 'error', 'msg' => "Gelieve uw bericht in te vullen."));
			exit();
		} else {

			//Send Mail
			$headers = 'From: ' . $mail .''. "\r\n".
			'Reply-To: '.$mail.'' . "\r\n" .
			'X-Mailer: PHP/' . phpversion();

			send_mail($to, $subject, $comment . "\r\n\n"  .'Naam: '.$name. "\r\n" .'Onderwerp: '.$onderwerp. "\r\n" .'Email: '.$mail, $headers);
		}

	} else {
		echo json_encode(array('info' => 'error', 'msg' => "Gelieve alle velden in te vullen."));
	}   

 ?>

               <form id="contact-form" method="post" action="contact.php">
                <div class="row contact-row">
                  <div class="col-md-6 contact-name">
                    <input name="name" id="name" type="text" placeholder="Uw naam*" required>
                  </div>
                  <div class="col-md-6 contact-email">
                    <input name="mail" id="mail" type="email" placeholder="Uw emailadres*" required>
                  </div>
                </div>
                <input name="onderwerp" id="onderwerp" type="text" placeholder="Onderwerp*" required> 
                <textarea name="comment" id="comment" placeholder="Uw bericht*" required></textarea>
                  <input type="submit" class="btn btn-lg btn-color btn-submit" value="Verstuur uw vraag" id="submit-message">
                  <div id="msg" class="message"></div>
                </form>