Bad Repair

I live in Wisconsin. I took my 98' Chevy 4x4 into a local GM garage to investigate a drive line noise. They said that the breather hose for the rear differential was sheared off and that water got into it and contamminating the fluid. They said they would have to pretty much rebuild the whole thing. I told them to go ahead with the repair. They had to replace bearings and seals, it cost me nearly $700 dollars to repair. 13 days later I am "upnorth" in the woods 150 miles from home and notice the rear differential leaking like pig. I managed to get the truck to the nearest shop. The mechanic there said it was put together improperly. I had to rent a vehicle to get home and to use for the week for work before I could get back up there to pick up my truck. Now this local GM garage refuses to pay for "anything" because I didnt take it to a GM garage. Any advice would be helpful.