Cartrack harassment for payment and not wanting to cancel contract after vehicle is sold

This places after service is pathetic and are only out to make money. The car that I had a tracker installed in I have sold and the new owner is not interested in having the tracker or taking over payments. I have Cartrack about this and they claiming i still have to make monthly payments. If i wish to stop monthly payments I need to pay a cancellation fee of over R2000. This is just ridiculous. I have since not paid them and they sending me messages of me owing them a R869 for the months I have not paid. I told them I am not paying further and I am not paying a cancelation fee either. The other alternative they gave me was for the tracker to be removed from the car that it is in and installed in the current car I have and this is not necessary as my current car has a tracker in. For them to remove the tracker and install it in another vehicle they again want me to pay for this. Since I have not been making payments they are trying every second day to debit my account costing me more money in bank fees. Your services are pathetic as this is a type of service that if the consumer does not pay, you just stop the tracking device from working again. I will never recommend you guys to anyone else or install one from your company again in any other car. I am sick and tired of you people phoning me and when i pick up nobody speaks and you drop the call. When someone does speak I will tell them im not paying and then the next day someone else will just phone me again regarding the same story.