DISGUSTING SERVICE EXPERIENCE!!!!

I am an ex-customer of Tracker's who sold the car that had the unit over a year and a half ago. I spoke to numerous people within Tracker to inform them that I no longer had the car and requested for the contract to be cancelled since the unit was already paid up. They have since failed to cancel the contract even after I paid the amounts billed after I had sold the car. My ITC credit profiles still reflect outstanding amounts billed recently and have now badly dented my credit score as well since for over a year I thought the account was closed so was not making any payments. I have read many similar complaints with Tracker debiting people's accounts who do not even have contracts with them anymore. This is not acceptable and could amount to a solid case in the court of law. I am really ****ed off and VERY FRUSTRATED!!!