php file to load on click button

I am loading the personalizetest.php (It has swiftmailer code to send an email) on click event. When I load it by clicking on the button in an html file with jquery code as given below, it works, and send an email. But when I add the same code in a php file in WordPress, and I click on the button, it says “action performed successfully” in console but I don’t get any email.

I searched a bit and find that I have to add following code in function.php to execute the file on WordPress which I did but now it is sending email on every page refresh. Either I open website or go from one page to another and not on button click. In short, I am loading this personalizetest.php file when I click the button with class=button:

function.php

<?php

function enqueue_scripts_styles_init() {


wp_enqueue_script( 'ajax-script', get_template_directory_uri().'./personalizetest.php', array('jquery'), 1.0 ); // jQuery will be included automatically
wp_localize_script( 'ajax-script', 'ajax_object', array( 'ajaxurl' => admin_url( 'admin-ajax.php' ) ) ); // setting ajaxurl
 }

  add_action('init', 'enqueue_scripts_styles_init');
?>

jQuery code

$(document).ready(function(){
$('.button').click(function(){
    var clickBtnValue = $(this).val();
    var ajaxurl = 'personalizetest.php',
    data =  {'action': clickBtnValue};
    $.post(ajaxurl, data, function (response) {
        // Response div goes here.
        console.log("action performed successfully");
    });
});

<input type="submit" class="button" name="insert" value="insert" />

personalizetest.php (Swiftmailer code)

 <?php

 require_once '/lib/config.php';
 require_once 'MyDecoratortest.php';


 function send_my_mail() {

 try {

//connect to database
$conn = new mysqli($root, $dbun, $dbps, $dbnm);

//get receipents
$recipients =[];
$sql = 'SELECT email, firstname, order_id,  FROM order_details order by _id desc limit 0, 1'; 
$result = $conn->query($sql);
$i = 0;
while ($row = $result->fetch_assoc()) {
     $recipients[$i]['email'] = $row['email'];
     $recipients[$i]['firstname'] = $row['firstname'];
     $recipients[$i]['order_id'] = $row['order_id'];
     $i++;    

 }


// create the transport
$transport = Swift_SmtpTransport::newInstance($smtp_server, 587, 'tls')
    ->setUsername($username)
    ->setPassword($password);
$mailer = Swift_Mailer::newInstance($transport);

// create and register decorator
$decorator = new Swift_Plugins_DecoratorPlugin(new MyDecorator($conn));
$mailer->registerPlugin($decorator);

//email
$html_message="My email text";

// prepare email message
$message = Swift_Message::newInstance()
    ->setSubject('Your Order at Dissertation Sage -- #order_id')
    ->setFrom($from)
    ->setBcc($bcc)
    ->setBody($html_message, 'text/html');


// tracking variables
$sent = 0;
$failures = [];

// send the personalized message to each recipient
foreach ($recipients as $recipient) {
    $message->setTo([$recipient['email'] => $recipient['firstname']]);
    $sent += $mailer->send($message);
  }

// display result
if ($sent) {
    echo "Number of emails sent: $sent<br>";
}
if ($failures) {
    echo "Couldn't send to the following addresses:<br>";
    foreach ($failures as $failure) {
        echo $failure . '<br>';
    }
    }
} catch (Exception $e) {
echo $e->getMessage();
}}?>