Why add a charge for deactivated device and a car that cartrack confirms it is not covered?

My 2 year contract with cartrack has expired. I received messages that my car is not covered and my device is deactivated but they attempt to debit my bank each and every month. Cartrack seems to be adding monthly charges each and every month and claims that I owe them. How can the service be deactivated and still be charged each and every month?