Poor customer service

My wife bought a car and had this tracker unit pre installed, that was fine as she agreed to keep it. 1 month goes by and no debit order from them, called to rectify and in addition.found out the number on the system was wrong. They said it was sorted, next month same thing, called various times still nothing. I was told to make a manual payment of which we will not do as we agree to debit orders cause time is of the essence, all the correct details were given on countless occasions and after that we chose to cancel and I refuse to pay cancellation fees and offered to pay for technician to come remove the unit. They disagreed and still keep sending collection agencies to call us. I sent them a messages to call us back with regard to this and still nothing. Tracker is useless and their customer service is one of the worst I've ever encountered.