Expired contract

I had 3 years contract with netstar with their tracking device then it was fine until my contract expired now am keep on receiving calls from credit worx saying am owing netstar I keep on saying same thing to them that my contract expired 3years ago but they so annoying keep on calling me with the same matter ,I blame my self to have contract with netstar cause no body call me for contract renewal as it was only for 3years that was our agreement if our contract is still valid let them challenge it to court of law am tired of being annoyed with their calls as if am owing them