Audi centre menlyn

About 3 months ago I took my vehicle in at audi centre menlyn to be assessed as it was skipping gears, the problem was the clutch. It was diagnosed by audi menlyn, the quote came down to about R27000 ,my insurance was covering only R16000 and I paid the rest. I got a call from them after paying the balance that the left control arm was bent and needed replacing, the quote came down to about R3300. After the vehicle was complete on the 11th of September 2019 as I was informed by audi menlyn I went to collect the vehicle on the 26th September 2019. As I drove out of their gate the vehicle started doing the exact same thing that it was taken in for repairs for in the first place. I immediately drove back inside the dealer for it to be checked. I was told that they would get back to me the next day. They then gave me a call the next day saying that the mechatronic component of the vehicle needed replacing and quote came down to R36000. After going back and forth with the manager about why that component was not diagnosed as damaged initially and them telling me that they would take the vehicle to some gearbox specialists to try and have the mechatronics unit fixed instead of replaced with no success they told me that it cannot be repaired it needs to be replaced and the cost would be R16000 at the gearbox specialist, after a few days I went to the dealer and instructed them to bring my vehicle back I will tow it away from their premises. They called me later on that day to tell me that they would pay R8000 and I must pay R 8000 of which I refused because I dont have such money laying around. I called them after about week and I was told I can pay R 6700 and the rest audi south Africa will cover.

My issue is why do I have to pay for this when the mechatronics unit was not damaged when I initially took the car in for repairs.

Please help