Wrong diagnosis

On the 8th February I took my Q5 to Audi Menlyn for gearbox malfunctioning and they fix it charged me R15,000. After 2 weeks same problem, same diagnosis and was told that they can't fix it. After putting pressure was told that Megatronics are damaged I must pay another R30,000+ to fix. To me it means they did wrong diagnosis in the first place now I'm expected to pay another R30,000 within a 2 weeks and my car is now out of motor plan. I could understand if they are prepared to take a blame and responsibility to say on the new quote they will deduct R15,000 that I already paid cause they don't know their job. This service is disgusting and coning of some sort, will never ever in my life associate myself with the brand, but also prepared to go to media for this kind of service and treatment.