defective products

On 08 September 2014 I bought a brand new Audi A4 TFSI. I noticed that it had an \uneven idling"problem. In November 2014 I reported the problem to the service advisor who booked the vehicle in for check-up on 12 December 2014. The vehicle was released to me on the same day with the instruction that I must bring it back on 12 January 2015. The service advisor informed me that their mechanic could not diagnose the cause of the problem. I delivered the vehicle to Audi Cape Town on 12 January 2015 and it remained with them until 06 February 2015. The service advisor phoned me to come and collect the vehicle and never gave me any report about the status of the vehicle and I assumed the problem was fixed. I drove the vehicle for few kilometres and noticed that the \""uneven idling\"" problem is still there. I immediately phoned the service advisor and alerted him about the persisting problem and he promised to call me back in two hours time but he never did. I dropped an email the following day but to no response. It is clear that the vehicle is defective and the manufacturer's dealer failed to fix it. Please assist. <br> <br> """