1999 Volkswagen Passat No power tocar

I recently got my car stolen, when it got stolen they took my battery and cut the cables to the to the battery, also taking out the driver door lock and ignition. So a mechanic I know fixed all that new battery cables ignition etc. Problem is my car worked fine for a day but when I went to start it the next day car was completely drained from all power no lights no noise when I try and start it. Now it works when I jump it from another car but when I turn the car off and try to get in it again same problem car is completely dead if anyone has any possible ideas or help I would be thankful