Very worried

I've been a car track customer for a number of years now. I have two vehicles covered by them. Over the last year what has been really annoying, frustrating and even very concerning is the fact that they keep calling me to take out a cartrack tracking device. I've spoken to them on numerous occasions and they even cancelled my subscription to marketing offers but they continue to call. My worry is if they can't track my mobile number as one of theirs how can I be sure they are tracking my vehicles properly. Sadly because I have a contract I can't even cancel with them. I disappointed and I don't feel my vehicles are safe with Cartrack.