Is it definitely engine? Could it be a gearbox or diff whine or a wheel bearing?
If its engine then I'd recommend a diagnostic check to see if any fault codes flag up
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.