Poor service delivery and bullying tactics

I had an excellent service with cartrack until my unit became faulty and I had to find that out myself after noumerous calls to their repairs department and them promising to get back to me failed I then decided to cancel their debit orders until I received a service from them they start calling in relation to my account being in arrears and I'm now being hassled by their collections department for a service I'm not receiving and I refuse to pay for the months where my tracking unit was inactive and I want a refund for the months where I paid but the unit was inactive.