damn, this shit is fucked up!
I had this same shit happen to me but I was lucky in the end.
I had my car in a autobody shop one time and when I came to pick up my car my stereo was gone. Nothing special, just a piece of shit cd player that was actually on its last leg anyway. Im assuming some tweeker that worked at the shop stole it, funny because the cd player was a piece of shit and wasn't worth hardly anything.
Well I go up in the body shop straight furious at them motherfuckers telling them they owe me for the cd player. The older salesmen who charged my insurance for the body work told me that They were not responsible for stolen merchandise in car. but in the end I still got the body shop to replace my cd player with a new alpine one which still works to this day.
I was lucky because I thought of it as a free upgrade from my old piece of shit cd player.
who knows, maybe enough bitching in their face will get them to buy you new shit to shut you up.
Keep showing your face at the body shop and maybe they will help you out to get rid of you.