Sorry to hear of your situation. Adams you've paid via eBay, then hopefully you should have some come back. As eBay are on the side of the buyer not the seller.
Have you tried Audi heritage?
Only problem is that they won't ship to the UK. So only way to get parts is if you have a fridge living in Europe who can ship the part to you.
Take a look at this thread. A fellow members had a similar issue 5 days ago.
https://www.audiownersclub.com/forums/topic/24553-bench-test-dash-cluster/
dpf and egr are the biggest risk factors. The after that turbo and injectors.
However well serviced diesel's can last along time.
My a6 c5 2.5tdi has never missed a service from new and been over serviced if anything. Before engine went bang it had covered 344k miles.
It was on its second turbo and original injectors.
I'm putting a replacement engine in it now.