You should take a copy of every contract you sign at the time you sign the contract. If you don’t have access to a copier, take a photo with your phone.
If there is no way at all for you to take a copy, initial and date every page.
These actions will stop the other party to the contract demanding you honour clauses not in the contract you signed. They could do this by writing new clauses and slipping those pages in so that when you ask to see the contact it looks like those clauses are in the contract.
Yes, sadly, this happens.