We sold the car with the tracker in and told cartrack now they say we have a 3year contract with them and if we want to cancel the tracker I have to pay R6000+

We sold the car with the tracker in and told cartrack now they say we have a 3year contract with them and if we want to cancel the tracker I have to pay R6000+ . Not only that the debt order goes of every month but they phone us 3 times a day saying I did not pay and they get very disrespectful with you if you try to explain that it already went off the bank account