If your Audi A3 TDI is in need of service, or has an issue and the dealership is not meeting your TDI needs, you may want to find a dealer alternative for service and repair.
The Audi dealership technician services gasoline vehicles 99% of the time, and they usually do not want to take the extra time to properly diagnose or repair a TDI vehicle that 1% of the time it is in their service bay. That is where a specialized service & repair shop like JA Autowerks in Shrewsbury, NJ falls into place.
Timing Belt service including a water pump with metal propellers or checking the final adjustment on the high pressure, common rail fuel pump is what sets a indie shop like JA Autowerks apart from the flat rate, rushing Audi dealership technician.
If you TDI has an issue, and you can not find a honest answer, shoot email@example.com an email and see if they can help you out.
I have never met John, but over at the TDI Club he has received quite a lot of positive reviews from happy customers. I certainly endorse his suggestion that you wean your Audi or VW from the dealership habit.