Black listed for a mal****ing tracking system

I got a call from altech net star offering me a tracking system in 2013 and I accepted the offer for the system to be installed. they installed the system after 2 days I called them to test the system then I was informed that the system is not functioning well. I was advised to return back the car to the installer then I did so. after 3 days again I called them to test the vehicle. I was informed that its still not functioning and I should return it back then I returned it back again. then after 2 days again I called them to test the signal and I was informed that its still not functioning I told them that I don't want the tracking device anymore as its not working and I will not be able to pay for a tracking system that is not working. then in June 2014 I got a call from debt collectors stating that they are calling on behalf on Altech net star. I was informed that I owe net star R 1600 and I must pay it. I told the debt collector that I will not pay as the system was not functioning. I was at the bank recently applying for finance then I was told that I was black list because of this account with net star.