Filing Gas Problem

Check the Canister Closed Valve (CCV) which can be stuck in a closed position. The canister can also be full or fuel or even water.

Check the vacuum lines between the fuel tank and the canister; between the CCV and the vacuum line for a blockage or restriction.  If anything restricts or stops the fumes/vapor from leaving the fuel tank and entering the charcoal canister, this can create a pressure problem.

The problem can also be a restriction in the fill tube or the vent valve.

Obviously you need to find the actual cause of the problem and fix it or have someone do that for you. Meanwhile, try to pump as slowly as possible and perhaps even change the angle at which you hold the gas pump nozzle when you put gas in the car.  (Although this shouldn't work any more, sometimes it does.)