Terrible service

Absolutely terrible service. Bought a new car there End of November. The car didn’t want to start on Thursday and everything was just dead. The AA came on towed it to the nearest branch. They say that it is a fuse at the battery that blew. Now they say that I must pay for it as the fuse was apparently tampered with. I don’t even know where the fuse is!!!! The car is under warranty and needs to be fixed by them. Nobody is getting back to me and I need this car for work.