Cartrack refusing to cancel duplicated contract

bought a car that had a unit from tracker which was paid up unit the dealership wasn't aware of, and they advise me to get a tracker. then i went to car tracker and requested a unit, their salesman instead of advising that there's unit on this car so i should just pay month to month on the unit already installed. then he went to add another unit and they were debitingme twice .when i enquire with them i was told im paying for 2 cars how i dnt know.they then told me my car has 2 units installed 1 paid up and the new one i told them to remove the new 1 and cancel the 3 year contract i will pay month to month on the paid up unit they refuese and submit my data to ITC and say i owe 3800 for mistake caused by their sales person