PHPMailer cannot be resolved - php

Question

So I am trying to set up a contact us page on a website i am creating but PHPMailer just refuses to work for me.
From what I can see, it just isn't recognizing the PHPMailer class at all and I am not really sure why. Here is my PHP code for the form to send the email, as far as i can tell i have correctly installed PHPMailer/Composer, and have done everything else correctly, but i still get errors when trying to use PHPMailer at all. "PHPMailer cannot resolved to a type" and "The import PHPMailer\PHPMailer\PHPMailer cannot be resolved"
<?php
use PHPMailer\PHPMailer\PHPMailer;
require_once './vendor/autoload.php';
// Bunch of code validating all the variables from the form
function send_mail($toEmail, $endSubject, $endMessage, $endName) {
$mail = new PHPMailer(true);
$mail->isSMTP();
$mail->Host = "smtp.domain.com";
$mail->SMTPAuth = true;
$mail->Username = "LOGIN EMAIL"; // Email
$mail->Password = "PASSWORD"; // Email password
$mail->SMTPSecure = "tls";
$mail->Port = "587";
$mail->From = "example#domain.com"; //RANDOM EMAIL TO SEND THESE MESSAGES TO OUR EMAIL
$mail->FromName = $endName; //CUSTOMERS NAME
$mail->addAddress($toEmail); //WHOEVER WE ARE SENDING THESE EMAILS TO
$mail->isHTML(true);
$uri = 'http://'. $_SERVER['HTTP_HOST'];
$mail->Subject = $endSubject;
$mail->Body = $endMessage;
if($mail->send()) {
return true;
} else {
return false;
}
}
?>