Poor client service

I had one of my company vehicles ****** before and after it was replaced decided to fit a Tracker and also added the tracetec unit, this was a very long time ago, I understood that the tracetec unit had a limited lifetime, and it would have to be replaced, this never happened as I decide to rather upgrade the tracker sytems on all my vehicles to work more effectively, I never cancelled my agreement with tracetec presuming that they would be honest enough to communicate with me that their unit is no longer effective and thus give me the option to cancel or replace, this did not happen however my debit order continued running, when I finally realised this and cancelled the debit order they are insisting that I still pay one months notice due to the cancellation agreement. My question is, I understand that part of my agreement is to pay, I also understand that part of their service which Im paying for is to track, I do not know in which vehicle this unit was placed or if I still even own this vehicle. I requested them to please notify me where my unit is and I will gladly pay... This has still not happened however I am continuously being threatened of not enjoying uninterrupted cover if I do not pay! Please proof to me I m still enjoying your cover and I will pay for it and follow the agreed terms of cancellation. Even though I am 90% sure you have been taking my monies over the past months if not years without being able to offer any form of service, you still want to milk me for the cancellation???