NHTSA Complaint #11449740 — 2001 AUDI S4

I took the vehicle into the dealer (Westwood Audi) for a Safety Recall repair as requested by Audi. It was for a Driver Front Airbag Inflator replacement. The work was done but when the car was returned the airbag warning light was on. I went back in to the service department and was told that the airbag module had failed and that the part was no longer available from Audi. An aftermarket part could be installed but I would have to pay for part and the repair. No cost estimate has been given. I called Audi of America and they said that the Dealer told them that they didn't break it so they will not cover the cost of repair. I have owned this car for 20 years and it is in exceptional condition. I took it to the Dealer in perfect condition for an airbag repair and got it back with an air bag warning light on and they say they didn't do it? Now I have a car without functioning airbags. Anything that you can do to help resolve this?