Cartrack worst tracking company ever!

One of the biggest mistakes I have ever done was taking a contract with cartrack, on different occasions they have failed to locate my car and the panic button was not working! Until I eventually joined a different tracking company and stopped paying car track! On a daily basis I get calls from their rude consultants! Who make empty promises about escalating the matter! I won't pay for services that were never rendered! Now that I stopped paying all of a sudden I am in breach of contract! Contract ended in March and the lady I spoke to this morning had the nerve to tell me I will continue with the contract! Is there a way to get cartrack to stop harassing me ?? Since they failed to render services and were in breach of contract?