Weirdest Email/Form Problem

I ran into the weirdest problem on a wordpress site I just created.

I made a custom email submission form on this page: https://fitms.org/request-an-appointment/

The form action runs a PHP script that I put in the directory /fitms/wp-content/themes/remag/php (I orginally had the script in the site root and I moved it there to see if it would fix the problem: it didn’t)

Here is the issue. As soon as the form-action php script is on the site, I immediately start getting an email once or twice per minute filled with random text. There is no way it is coming from a spammer because it literally started the second I uploaded the file. The emails keep coming and coming until I remove the php file. WHY IS THIS HAPPENING??

Here are the emails I get:

Someone has scheduled an appointment using the fitMS Website Form

[ SPAM content redacted again ]
Type of Appointment:

(notice they all come from a random @outlook.com email address)

Here is the code in my PHP script. I added the ‘prove you are human’ 2+2 =4 thing to stop the emails from coming. It has fixed the problem but I still need to know what was causing that and I’d imagine the server is still running the script so it is constantly wasting server resources.

<?php
$name = $_POST['name'];
$email = $_POST['email'];
$phone = $_POST['phone'];
$datetime = $_POST['datetime'];
$service = $_POST['typeoptions'];
$math = $_POST['math'];

//setup email
$headers = "From: fitMS Website Server <>\n";

$headers .= "Content-Type: text/plain; charset=iso-8859-1\n"; 

if ($service == 'massage'){
	$recipient = "XXXXX, XXXXX, XXXXX";
}
elseif ($service == 'chiropractic' || $service == 'nutrition' || $service == 'food-sensitivity' || $service == 'acupuncture'){
	$recipient = "XXXXX, XXXXXX, XXXXXX";
}
else {
	$recipient = "XXXXX,XXXXXXX";
}

$subject = "fitMS Appointment Scheduled Online";

$message = "Someone has scheduled an appointment using the fitMS Website Form\n\nName: ".$name."\nEmail: ".$email."\nPhone: ".$phone."\nPreferred Date/Time: ".$datetime."\nType of Appointment: ".$service."\n\n\n\n";

if ($math == "4" || $math == "four" || $math == " four" || $math == " 4"){

mail($recipient, $subject, stripslashes($message), $headers);
}

header( 'Location: https://www.fitms.org/thank-you' );

?>

Please give any suggestions/theories and I really appreciate the help!

-Tim