Car track

I installed a car track in my car. From the first day they installed the tracker it did not function correctly. I receive a SMS from them that the unit is not functioning and they have to come and replays the unit. After weeks someone came out to replace the unit. I phoned car track and ask them they must activate the early warning so that I can know if some one took the car. They also did not do that. I received another sms from car track that state that the unit is not working and I have to call them so that they can come out and replace the unit again. After 20 phone calls I told them that they must come and take out their unit because still its not working. They just put the phone down in my ear and send me a invoice every month that I have to pay. Today I phoned them again now they say I have to pay a cancellation fee of R1570 for them to come and take out the unit. I am not going to pay that money as the unit did not function at all for so long. I even took out the battery and only 3 hour later they informed me that the car is down. Please help with this hello peter