The worst and I'm cancelling them

Guys in April 2019 I sold my car Kia Rio and phoned tracker to cancel which they did,and also same month I bought another and phoned them again to install a new unit,ok fast forward to October they contact me saying I drive o high risk vehicle and they need to install second device which is free of charge,they did that and them month end I notice they double debit me,I call and ask what's happening they tell me there is another car with a different reg,I tell them I don't own a second car and they said okay they will cancel,them I get an email saying m liable to pay for the second car,I tell them I can't pay for some I don't know,ok cool then November again they double debit me again and I call to ask what happening,they telling when second device was installed it picked up another one that was used before on the car by the previous owner,and I asked why are they charging me for that cos u have only one device with them,lady tells me I'm liable becos I did change of ownership, because now I want my money back