Unhappy customer

I am truly not happy with the service I received from netstar. I traded in a car for a new one and called them, the person assisting me advised me that I can reinstall the device to the new car rather than cancelling the contract and restarting to avoid paying for cancellation. So they came to install a new device and we didn’t use the old device from the old car. When I checked the statement for June it showed that I had to pay for the old car’s device, the new device and the installation fee. I called in to correct this and Thokozane from retention said it was sorted and I won’t have to pay for cancellation for the first device. Now I received my invoice for July and it’s still showing the old car and I have to pay, I call in again and the guy at the retention says I have to pay the cancellation fees. I’m truly not happy with the back and forth.