New member and sport diff fault

Hi I’m Chris and new to the forum and new to my dream car rs6 7.5 although it’s soon turning into a nightmare so I’m really hoping someone can point me in the right direction 

I had a sports diff fault come up while when plugged in to vcds said it was a oil pressure fault so I booked the car into vasstech which they said it needed a new oil pump and diverted valve which they fit but then said it wouldn’t let them code it and that it had to go to Audi which after a 4 week wait it has just been in and they are saying they have coded the new parts but it’s still got a coding message in there that they can’t get rid of so the car still has a sports diff fault on the dash ant they are advising the electronic side of the diff is faulty and needs a new diff at a cost of £14500 which is a no go , does anyone know anywhere that can repair these diffs or even just someone a bit clues up that could have a go at coding it again for me ?

im in North Yorkshire but can travel if anyone can help me out 

Sorry if this is in the wrong section 

thanks