How to verify payment by user via xml db before rendering dynamic image

I am pulling my hair out trying to create an If statement that will check an xml file to see if a person has submitted a payment within the last 30 days.

I have a PHP file that will display information from an xml file as a .png. Before that image renders I would like to run an If statement against another xml file to see if the person has paid in the last 30 days. Basically if I have a payment $from $username (these would be matching eg $from= bob and $username= bob) and the $date is within the 30days then display dynamic image else display a different image.

EDIT: I'm not quite sure if it matters but this will be located in the same file that generates a dynamic PNG via PHP.

Here is an example of the payment database.

<PaymentsByMonthYear>
  <Payment>
   <Id>51180698</Id>
   <Date>2015/02/02 15:23:27</Date>
   <To>Company</To>
   <From>Jim</From>
   <Amount>1000.00</Amount>
   <Location>null</Location>
   <Comment>null</Comment>
 </Payment>
  <Payment>
   <Id>51180698</Id>
   <Date>2015/01/15 15:23:27</Date>
   <To>Company</To>
   <From>Bob</From>
   <Amount>1000.00</Amount>
   <Location>null</Location>
   <Comment>null</Comment>
 </Payment>
  <Payment>
   <Id>51180698</Id>
   <Date>2014/12/02 15:23:27</Date>
   <To>Company</To>
   <From>Steve</From>
   <Amount>1000.00</Amount>
   <Location>null</Location>
   <Comment>null</Comment>
 </Payment>

So far all I have that reliably works is the connection to the XML file

<?php

  //Check payment
  //Connect to payment server
  $link = "http://ift.tt/1LEuv6w";
  $xml = simplexml_load_file($link) or die("Error: Cannot create object");

  //Gather Fields
  foreach($xml->children() as $payment_info)
   {
   $date = $payment_info->Date;
   $from = $payment_info->From;
   $amount = $payment_info->Amount;
   }

All i really need to verify is that a payment was made by the person trying to access the file, and possibly the amount in the future.

Thanks a lot for any help!