This happened to me. It was a Mitsubishi dealership and a bus had hit the car - every panel was bent and every window shattered - it was a mess but repairable and the chassis was fine.
After 6 months nothing had been done - it just sat there. So I went in with the wife, to talk to the service manager - got the usual brush off - and so went off to find the GM. Two people scurried off, so I followed where they went. They went to the offices and came out saying "she's not here" - so I went where they'd come back from and Lo and Behold, the GM (owners daughter) was sitting right there in her office.
We explained it and at first she couldn't believe that a car could be there so long. Upshot was - she gave us her own car as a loaner (a bit hello kitty for me) and fired the manager in charge of repairs as he'd been taking bribes to jump the queue.
We never got to play our trump card which was a report to some consumer bureau that covers the motor industry, which is available and I can find the details off the wife if you need them.
But next step - see the GM of the place - it's possible they don't even knoe about it.