Disfuntional device from netstar

I had my car installed with a panic button of which ther device is not working as I have been testing it time and again checking if something happens I will be covered or rescued, after testing or pressing the panic button no one will phone me, I am being told I have been handed to Nimble debt collectors. I was asked to pay an amount of money which I did without acknowlement that the account has been paid infull. After all this payments I emailed netstar and asked them to cancel and come and remove their disfunctional device from my car. They send me an email to tell me I owe them money, the email is from nimble debt collectors. I can't pay for something that is not working. I ask for removal of the device.