Tracker will not cancel policy

I've been trying to cancel the tracker on a car that I've sold, it is an impossible exercise, they answer the phone for new contracts quickly but have not once answered any of my calls for cancelation in the last week and a half. I spoke to 2 consultants who told me that the request for cancelation has been logged and that I would get a call back, I have not received a single call back or e-mail. Scary that I trusted a company that operates like this with my safety and the safety of my family.