Cartrack account woes.

I bought a car from Carzuka (a wholly owned subsidiary of Cartrack and now, apparently out of business) At the time a cartrack contract was signed. Unfortunately the car never worked properly and I was informed by the salesman that they were not prepared to pay for repairs (including a non functioning battery, electrical system malfunctions etc etc) Ultimately the vehicle was sold to me under false pretentions as it did not perform the function that I bought it for. I wrote to cartrack and told them that as the car did not function, There was no point in having a tracker unit attached. I received no reply. They attempted to debit my account and each time I reversed the payment. Ultimately their lawyers became involved and offered me a discount, which I, reluctantly paid, merely to close this matter. I am now having attempts to debit my account again and have received harassment calls from their accounts. Since I have lost the cash value of the car I bought and settled with the lawyers, I am prepared to leave this alone, however they are still attempting to charge me for a non existent service.