paid for nothing

I took ownership of a car fitted with a netstar tracker, I moved the account to my name. months later I discovered the unit is not operational, netstar could not even tell me, when was the last time they were able to track the car, so all this time I have been paying for a service that was never rendered. they insist according to the contract I am responsible for testing the unit, the contract that was never sent to me, I have contacted them many times asking for the proof of that contract that was given to me, their agents would put me on hold for over 20 minutes then hang up the line, finally when I spoke to their manager and insisted that I need that proof of that contract she just sent me a welcome letter with the current date and incorrect info of mine. how can an early unit tacking device not report to your system for months if not years and you can't even pick that up or alert your customers while you happily debit their account?.