What's wrong with contact page? I keep getting this message " Could not instantiate mail function."

<?php 

require_once("../inc/config.php");

if ($_SERVER["REQUEST_METHOD"] == "POST") {
    $name = trim($_POST["name"]);
    $email = trim($_POST["email"]);
    $message = trim($_POST["message"]);

    if ($name == "" OR $email == "" OR $message == "") {
        $error_message = "You must specify a value for name, email address, and message.";
    }

    if (!isset($error_message)) {
        foreach( $_POST as $value ){
            if( stripos($value,'Content-Type:') !== FALSE ){
                $error_message = "There was a problem with the information you entered.";
            }
        }
    }

    if (!isset($error_message) && $_POST["address"] != "") {
        $error_message = "Your form submission has an error.";
    }

    require_once(ROOT_PATH . "inc/phpmailer/class.phpmailer.php");
    $mail = new PHPMailer();

    if (!isset($error_message) && !$mail->ValidateAddress($email)){
        $error_message = "You must specify a valid email address.";
    }

    if (!isset($error_message)) {
        $email_body = "";
        $email_body = $email_body . "Name: " . $name . "<br>";
        $email_body = $email_body . "Email: " . $email . "<br>";
        $email_body = $email_body . "Message: " . $message;

        $mail->SetFrom($email, $name);
        $address = "miguelbpa13@gmail.com";
        $mail->AddAddress($address, "Shirts 4 Mike");
        $mail->Subject    = "Shirts 4 Mike Contact Form Submission | " . $name;
        $mail->MsgHTML($email_body); 

        if($mail->Send()) {
            header("Location: " . BASE_URL . "contact/?status=thanks");
            exit;
        } else {
          $error_message = "There was a problem sending the email: " . $mail->ErrorInfo;
        }

    }
}

?><?php 
$pageTitle = "Contact Mike";
$section = "contact";
include(ROOT_PATH . 'inc/header.php'); ?>

    <div class="section page">

        <div class="wrapper">

            <h1>Contact</h1>

            <?php if (isset($_GET["status"]) AND $_GET["status"] == "thanks") { ?>
                <p>Thanks for the email! I&rsquo;ll be in touch shortly!</p>
            <?php } else { ?>

                <?php
                    if (!isset($error_message)) {
                        echo '<p>I&rsquo;d love to hear from you! Complete the form to send me an email.</p>';
                    } else {
                        echo '<p class="message">' . $error_message . '</p>';
                    }
                ?>

                <form method="post" action="<?php echo BASE_URL; ?>contact/">

                    <table>
                        <tr>
                            <th>
                                <label for="name">Name</label>
                            </th>
                            <td>
                                <input type="text" name="name" id="name" value="<?php if (isset($name)) { echo htmlspecialchars($name); } ?>">
                            </td>
                        </tr>
                        <tr>
                            <th>
                                <label for="email">Email</label>
                            </th>
                            <td>
                                <input type="text" name="email" id="email" value="<?php if(isset($email)) { echo htmlspecialchars($email); } ?>">
                            </td>
                        </tr>
                        <tr>
                            <th>
                                <label for="message">Message</label>
                            </th>
                            <td>
                                <textarea name="message" id="message"><?php if (isset($message)) { echo htmlspecialchars($message); } ?></textarea>
                            </td>
                        </tr> 
                        <tr style="display: none;">
                            <th>
                                <label for="address">Address</label>
                            </th>
                            <td>
                                <input type="text" name="address" id="address">
                                <p>Humans (and frogs): please leave this field blank.</p>
                            </td>
                        </tr>                   
                    </table>
                    <input type="submit" value="Send">

                </form>

            <?php } ?>

        </div>

    </div>

<?php include(ROOT_PATH . 'inc/footer.php') ?>