Engine light on cause gas cap, it continues appearing, what to do? on 1996 Pontiac Sunfire

I change the gas cap, fix, tighten fix, but continuos appearing, I continue resetting the code any solutions.

Asked by for the 1996 Pontiac Sunfire
The EVAP system needs to be tested, The information the computer is receiving from the test is not holding a preset tolerance for a properly sealed system. It is recognizing there must be a gas cap issue because of the information it has received is a very large leak. Obviously it's not the gas cap.