2002 Cadillac Deville Does the radio control the electrical

Computer problem
2002 Cadillac Deville Automatic 59000+ miles

I had my car in the shop for 2 1/2 weeks at a service station gargage to determine what was causing the battery to drain after having jumped it twice and rhen replacing it. Finally they determined that they needed to replace the "instrument cluster" and did so. The part cost $445 and with labor and tax the total was $861.57. I picked the car up on a Fri. And Sat. It didn't start. The garage was closed, so they picked the car up on a Monday and called Tues. To tell me that they think the radio had caused the short in the "instrument cluster" and that it could be fixed by disconnecting the radio. By then, they had had the car almost 3 weeks so I told them I had to have it back so go ahead. I picked the car up on Weds. And they had cut the radio wres. Also, none of the interior lights are working. They had suggested that they might be able to find a second hand radio to replace it (at my expense). I am a 77 yr. Old widow, and I think they "saw me coming." I called Mastercard and they are witholding payment on the charge until an investigation is conducted. If it were the radio, shouldn't that have been checked in the first place? Thanks for your help!