Car track is harassing me!!!

I’ve been harassed by Cartrack since last year and now I’m fed up!!! They sent me an sms to notify me of the faulty system they discovered and I should call to make an appointment, I did so immediately and they gave me a run around for months, I think I made over 50 calls to them being transferred from 1 line to another with my airtime! Still they couldn’t give me an appointment to fix the device and I called one time to see if they can pick up my location, they still couldn’t, that was probably 3 months later... I then reversed all their debit orders for the months when the system wasn’t actively working. As soon as they realized that they started to call me, I said to them I can’t be paying them for a system that isn’t working and whilst it’s them who are failing to fix it, I had to get another system installed from a different company as I can’t be driving around Joburg without all the safety precautions I should have in my car . They’re finance department has been harassing me since saying I owe them money for the 3 months I believe I wasn’t being serviced by them for as they should have been as per our contract. They called me again saying they are allowing me now to be released from their contract but they want to take out the faulty system from My car and change the ownership, which I was happy to do. To my surprise I’m still getting emails and calls everyday saying I should pay them the money I reversed and now they are resorting to handing me over to the credit bureaus. They are a **** and their service is zero!!!!!!!!!! I regret the day I allowed them to install their product in my car!!!