I, like you, have been turned away from TPS but 18 months ago so you’ve done better than me! Its the internal politics of VW / Audi!!
I was wary of using the dealers, Skoda in my case 18months ago, but they price matched (without asking) Quantum longlife oil which put my concerns to rest. Just go in armed with rough prices of what you need so you can sense check.
Last service before I sold the Superb I used Bosch parts and they were fine. While under warranty you should always use genuine parts.