1998 Chevy Silverado fuel tank collapsed

Evidently they didn't do the job correctly and I would take it back and tell them to fix it again at their cost as you have already paid for it to be fixed and it was not fixed correctly. There is a vent problem either with the purge system could be a clogged return line. Or could be something not hooked up. The fuel pump is pulling pressure out of the tank but you have no return pressure and this is causing the tank to collapse. Make them fix it or take them to small claims court.