Ryan.A6

Help is needed first ever post let's dive straight in..I have a A6 s line 2.0 tdi full service and well looked after an all that, I was pulling my caravan when the low oil pressure light came on and the engine lost some power and didn't sound the best so pulled over and got the car towed to audi my thought was the pick up pipe blocked but audi said they pressure tested the pump and that's ok and there not exactly sure what it is but said they can investigate for £1100 and thats when i declined. The knocking sounds like its high in the engine what should i do next the car is to good for the scrap heap has anybody had similar issues and how did you solve it your help I'll be much appreciated Since getting the car back I've changed the oil + filter but its not made much of a difference Thanks Ryan