New car aircon cannot be fixed by dealership

I bought a new VW polo from Cape City VW dealership in May 2014. Since Feb 15, a loud humming noise occurs when the aircon is turned on. I have taken the car to Cape City 3 times to look into this problem. Each time a new part was replaced, incl. the condenser, but the problem has never been resolved and the noise has returned. In Feb 16 I took the car into Claremont VW to look into this problem. Within a day I was informed that the cause was a leaking low pressure valve which they replaced. When I went to pick up my car I found that when driving, I could hear the noise instantly again. I asked to speak with the mechanic who worked on the car to listen while driving the car. The mechanic then gave a different reason for this fault (from the initial diagnosis) and told me that it is the compressor that needs to be replaced &amp; that it is due to a faulty batch of compressors that were fitted in the factory. <br> <br> As a new car owner, I never expected to buy a car that was manufactured with a faulty part and I am very disappointed. Now that I have taken the car in to be diagnosed on 4 separate occasions to 2 different dealerships I am losing faith in VW completely.