incorrect billing

I previously had 2 vehicles installed with a Tracker. In September, I sent Tracker an email to remove vehicle 2 and add on a new vehicle as I had sold vehicle 2 and purchased a new vehicle. They miraculously managed to add the new vehicle but have been debiting my account since September for the vehicle which I sold. upon contacting them, they advised that they were \investigating"and later that they would refund me(response only happened in December). But they have still managed to debit my account incorrectly in December for 3 vehicles And I have received no refund(4 months of incorrect debiting). This is not the first time that Tracker has incorrectly billed me. Please be wary guys - I am currently looking at moving service providers - I would rather use someone who won't rob me in broad daylight! !!"""