Benefit of the doubt, maybe the guy answering the phone looked out the window, didn't see the truck, and thought that meant it was in the bay?Man what a shit show. The fact the guy lied to you saying it was being worked on while it was stolen would have me talking to a lawyer
Good luck
I had a friend who had a similar thing happen at a chain store mechanic. Guy doing the brakes forgot to bleed them and proceeded to crash the car into a block wall right in front of us. Her local insurance agent did a lot of fighting for her, and got her more money than I thought the old car was worth. I think the store even paid for a rental until she found a new car.
I'm curious about the keys to your truck, and if they were left in the vehicle. If so, in my mind, that would be pretty irresponsible of them. Even if you signed away their liability, I'd think that they would be expected to take reasonable precautions to prevent theft?