BMW South Africa and Audi South Africa

I bought an Audi Q7 from BMW Sandton in June. I mentioned that the car was hesitating to start, we took it to Audi to check it out and Audi said the battery was fine. In September the car would no longer start and had to be towed. it is now Novemember and I am still without while everyone passes the buck on who is liable for the costs. DP and Used Cars manager at BMW refuse to return my emails or accept a meeting request. Audi South Africa have basically said pay R100,000 for repairs and we will not show any good faith for not picking up the issue. I also requested a meeting with their DP and they say it is not necessary. so less than 6months after buying a car I am now facing R100,000 of mechanical repairs.