Mailer send error when completing the form correctly

<article>
<?php if (isset($_GET["status"]) && $_GET["status"] == "thanks") {
    echo "<div class='thanks text-center'>
           <h2 class='uppercase'>Thank you</h2>
           <p>Thanks for your enquiry. We have received your message and will contact you shortly to discuss your requirements in more detail.</p>
           <p>Have a great day!</p>
           </div>";
    } else { ?>
<div class="intro text-center">
    <h2 class="uppercase">Give us a call or just pop in!</h2>
    <p>Please use the form below to get in touch with us. If you are making an enquiry about a car body repair, try to give us as much detail as you can. It will help us to get a better idea of the extent of any damage. You can also upload a photo showing the area where the work is required.</p>

  <p>If you would prefer to pop in, that's fine too. All we would ask is that you give us a call to check we're not in the middle of spraying cars when you arrive.</p>
</div>
    <div class="contact-form">
        <?php
        if(isset($error_message)) {
            echo "<p class='message'>". $error_message . "</p>";
        } else {
            echo "<div class='form-title'>
            <h1>Tell us what you need doing :)</h1>
            <h4>Describe your need and we'll get back to you asap!</h4>
            </div>";    
            }
            ?>
<form role="form" method="post" action="contact-us.php">
    <input class="text-input" id="name" type="text" name="name" placeholder="Your Name (required)" value="<?php if(isset($name)) { echo $name; } ?>">
    <input class="text-input" id="telephone" type="text" name="telephone" placeholder="Phone Number (required)" value="<?php if(isset($telephone)) { echo $telephone; } ?>">
    <input class="text-input" id="email" type="text" name="email" placeholder="Your Email" value="<?php if(isset($email)) { echo $email; } ?>">
    <input class="text-input" id="cardetails" type="text" name="cardetails" placeholder="Make/Model of Car (required)" value="<?php if(isset($cardetails)) { echo $cardetails; } ?>">
    <input class="text-input" id="claim" type="text" name="claim" placeholder="Insuance Claim or Private (required)" value="<?php if(isset($claim)) { echo $claim; } ?>">
    <input style="display: none" class="text-input" id="mileage" type="text" name="mileage" placeholder="Leave this field blank.">
    <input class="text-input" id="reg" type="text" name="reg" placeholder="Vehicle Registration" value="<?php if(isset($reg)) { echo $reg; } ?>">
    <textarea id="message" name="message" placeholder="Please describe your requirements in as much detail as possible. This will help us to better understand the extent of any repairs.  (required)">
<?php
    if(isset($message)) { 
        echo htmlspecialchars($message); 
    } 
    ?>
    </textarea>
        <button name="submit" type="submit" id="submit">Once you're done, push the button!</button> 
</form>
<?php } ?>
</div>
</article>