Bad service at Audi Centurion

They can't get my Audi A4 2013 gearbox right. It has now been 3 months, yes can you believe it 3 MONTHS and it is still not fixed! This is has become a nightmare, the service manager at Audi Centurion keep on making promises week after week. My car has been at Audi Centurion for a month, then at Audi Mayville for about a month and is now at Autobox in Koedoe****rt. They are now trying the 3rd recon gearbox but still no results. Looks like the expertise required to repair a Multitronic just does not exist in South Africa. What am I to do now after 3 months of no results. I can't sell it until it is fixed. Who can I use to take the car and fix it? The service from Audi on this matter is the worst I have seen.

Very frustrated, Ben