It actually turns out that the could not fix it since Schwinn does not sell replacement hubs, and that they were not a Schwinn dealer, but they still helped me. I ended up buying a whole new rear wheel from
Home - Choppers U.S., LLC. Then I brought the new wheel and old wheel back to the bike shop for them to match the freewheel and install a new one on the new wheel. They don't seem to mind that my repairs are for a motorized bike, in fact they complement me on converting a regular bike into a motorbike. I guess I am lucky to find a dependable bike shop to go to if need be.