Billed for an a car that I no longer have

I used to have a BMW and had a tracker installed by my insurance months later I cancelled the insurance and sold the car and was told that I needed to pay R1920.00 for the tracker and close off my account but now 2 years later they now say I have to pay a cancellation fee of about R1200.00 to have the account closed or have someone else takeover my tracker(the one I don't have) my question is how can this be they handed over the account to their agents and successfully collected the amount 2 years late but still on contract with them? please sort this mess out.