Charge for no service at all

Netstar is charging me for a device that is not working. I phoned in many times to let them fix it but till today. When I try to cancel they say it fine but I have pay for the installed device, mind you it's a device that is not working. I am sick and tired of their service. Pls ask them to track where is my car, I bet they won't be able to tell. Useless is how I describe them and their service. Good at threatening me so far