PHP Form not submitting on php despite working on html - php

Question

When I try and submit a form here (php page) - http://portsdownhb.ogdigital.co.uk/ the page throws the error 'Failed to load resource: the server responded with a status of 404 (Not Found)' when pressing submit, despite the exact same working on a HTML page.
The error suggests the page http://portsdownhb.ogdigital.co.uk/contact-us/contact.php is trying to be found but it should be http://portsdownhb.ogdigital.co.uk/contact.php
$(function () {
$('#contact-form').validator();
$('#contact-form').on('submit', function (e) {
if (!e.isDefaultPrevented()) {
var url = "contact.php";
$.ajax({
type: "POST",
url: url,
data: $(this).serialize(),
success: function (data)
{
var messageAlert = 'alert-' + data.type;
var messageText = data.message;
var alertBox = '<div class="alert ' + messageAlert + ' alert-dismissable"><button type="button" class="close" data-dismiss="alert" aria-hidden="true">×</button>' + messageText + '</div>';
if (messageAlert && messageText) {
$('#contact-form').find('.messages').html(alertBox);
$('#contact-form')[0].reset();
}
}
});
return false;
}
})
});
<form id="contact-form" method="post" action="contact.php" role="form">
<div class="messages"></div>
<div class="controls">
<div class="row">
<div class="col-sm-12">
<div class="form-group">
<input id="form_name" type="text" name="name" class="form-control" placeholder="First Name" required="required" data-error="Name is required.">
<div class="help-block with-errors"></div>
</div>
</div>
<div class="col-sm-12">
<div class="form-group">
<input id="form_email" type="email" name="email" class="form-control" placeholder="Email" required="required" data-error="Valid email is required.">
<div class="help-block with-errors"></div>
</div>
</div>
</div>
<div class="row">
<div class="col-sm-12">
<div class="form-group">
<textarea id="form_message" name="message" class="form-control" placeholder="Message" rows="4" required="required" data-error="Please, leave us a message."></textarea>
<div class="help-block with-errors"></div>
</div>
</div>
</div>
<div class="row">
<div class="col-sm-12">
<div class="g-recaptcha" data-sitekey="****"></div>
</div>
</div>
<div class="row">
<div class="col-sm-12">
<input type="submit" class="btn btn-success btn-send" value="Send message">
</div>
</div>
</div>
</form>