How to repair Leaking Shower Stall?

After a house fire last year, the contractor who did the repair installed two new shower stalls. Both are leaking. Due to heavy smoke damage, the sheet rock in the entire house was removed down to the studs and the tub/shower unit/stall was replaced with new. They are 4 piece units, consisting of the tub, and 3 wall pieces (front, side and back piece). Ever since we moved back into house (approx. 3 months) the showers have leaked. It is so bad the sheetrock is wet and has caused a hole to develop. The wet area in the sheetrock is at both ends of the tub/shower unit where the shower walls sit/meet the tub unit then it runs out of the sides into the sheetrock. The sheet rock tape is actually falling away from the wall.
The contractor and I have both caulked, then removed old and recaulked the tub letting it set for 4-5 days at a time several times. And the contractor installed shower doors in an attempt to stop the leak. The contractor even suggested the leak is due to my families shower habits, which is obsured because, both showers leak at the same place - at the shower joint. If it was water splashing off our bodies as we shower it would be on the floor, all over the walls, everywhere, but it's not. Both showers leak at the same place where the walls run down and sit on the tub area then out to the side. We have tried to fix it, but the leak is still there. Any suggestions?