Cartrack issue

I called to advise the cartrack that I have sold my vehicle and the owner took out another contract for the same car. When I told them I wanted to cancel, I was told to pay R1700. I then said I can't pay for something I don't own. The consultant then told me that I can move the unit to another car and I said I didn't have another car then. I was not told of the de-installation fee instead learnt about it today after I called to make follow up. Cartrack is just ripping us off ....If they punch in my old car's vehicle reg number, they should be able to see or note that the car has a device already. I find this very unfair and extremely wrong.