Bad service from cartrack

I got a tracker installed in my vehicle being a Mercedes Benz by cartrack somewhere last year but when I check on the app it always gave me wrong or inaccurate position to were my car is. I reported these to them but they demanded that I paid another fees to them to can come and fix it, though I explained to them that their unit was defective hence it couldn’t show the accuracy position of my vehicle and they admitted it but on messages they used to send to me was to say that the unit was tested and found to be working, which is lies.

It worries me because they debited my account every month and not rendering the service I expected from them and what they are doing is tantamount to theft as they are not honest and wanting money for their own incompetence.