Unfair treatment

On month end April 2015 I purchased a C200 mercedes benz 2014 model from Pietermaritzburg (Gorden City Motors), reg no is NP 166675. The car has two USB pots. One time I noticed that the radio does not read the USB but some times it reads. I reported the problem to Mercedes Benz imediately and the car was booked in on the 9 September 2015. the report I got from one of the service consultants was that Mercedes Benz will not cover my problem. I said to this consultant the car is fairly new and that USB pot cannot just break or fail soon because the blame is pushed on me. The same consultant said its he will talk to warranty manager. Later he called me to say they will order the part and call the car in when they receive this broken part. The same consultant call to give phone number for mercedes benz warranty (0800....). On the 14 September 2014 I phoned this number, the person I spoken to took my car reg no and promised to call back but he never called me back. It is very unclear to that I buy a car then within 4 months the car radio gives me problem and they want me to pay, why is it like that? Please I ask this to be resolved unless they do not car about their customers.