Bad service received at Audi Centurion

I’m so disappointed in Audi South Africa! I bought an Audi A5 2.0TDI 2019 model on the 12th of July 2019 as brand new at Audi Rivonia. On 23rd November 2019 the car broke down at night around 23:00 on N14 towards Krugersdorp I called Audi road assistance and they sent a breakdown 2hours later, they towed the car to the nearest dealership which is Centurion Audi Centre. When we got there security wouldn’t open for the breakdown so they had to store it at their yard until Monday 25th November. On Tuesday I received an email from Audi stating that their service advisor will contact me on Wednesday so that they can start with the diagnosis on the car. The service advisor indeed called me and they started on the car, now he starts asking me do I know how diesel looks like, I told him I don’t know. He said I put petrol on a diesel car and I told him it was highly impossible I even went to take footages at the garage now they say diesel was contaminated. How should I know contaminated fuel? They say warranty and motor plan won’t cover for the damage it’s considered negligence so I went back to the garage and they sent their agents to Audi to take samples of the diesel in the tank. They took the diesel to the laboratory to be tested and they say there’s no contamination on the fuel and immediately I called Audi South Africa to my surprise the case is closed but I can open it up again they won’t even give me a courtesy car it’s been two weeks I’m walking but I’m paying every month for the car. They now send me a quote of R129928.50 who’s supposed to pay that? Instead of diagnosing the car they speculate. I think I must involve the bank now tell them I no longer want that car