Cartrack/Nimble Collection Service HARASSMENT

Three years back i've bought a new vehicle I've informed cartrack to please come and remove the device from my old vehicle and to put it into the new vehicle as the old vehicle will be in my yard for two weeks after I've sold it. Cartrack failed to do so they failed to reply to me numerous emails and calls, so I decided to stop the debit order as I cannot afford to pay for something I don't get. Since then Cartrack and this Nimble collection services is harassing me with threats and emails. They don't even suggest a solution to the problem by saying they'll install a device in my new car and the service can go on for the remainder of the period, they just from the day I cancelled the debit order until today 3 years later harras me,