That doesn't sound right. They must not have understood the question... Let me help you make this easier for them.
I created this page: http://www.arisbeststeakhouse.com/debug.php
It is a single line of code that causes an error so that session variables won't work on your site. Show that page to the hosting provider's support team and ask them to fix that problem without upgrading the php version or hosting plan. I don't see how they can claim that is outside of the scope of your plan at that point.