Bad bad service (Cant call it bad if there is no service)

I got a tracker 3 years ago. They called me a year ago and said they need to replace the unit free of charge as theres issues with this unit. I said its fine. Now I sold the car and want to cancel. they said theres a year left on contract. Crazy after I did not ask for a new unit. They said they wil get recording and its a month later. no one replies to me. Send so many mails. now I dont know how to cancel. Ive never seen any service like this