BILLED AND TAKEN TO LAWYERS FOR CAR TRACKER OF A CAR I NO LONGER OWN FOR OVER A YEAR

Last year around June/July I contacted Car tracker letting them know to cancel my contract as I had traded for a new vehicle,I had already had an outstanding amount which I had made payment arrangements with,which at a time was R450,to my suprised contract was not cancelled and they continue to bill me,I’ve been receiving calls saying I’m being handed over for not paying cancellation fee which is now R3900,how’s this even possible??Please cancel my membership and stop ruining my name it’s affecting my credit score!!