No follow up done

I have been with Cartrack for over 7 years and this year I got rid of the car that was under them. I tried to call and cancel with them with no success since February and I ended up sending an email on the 4th of August, they responded saying that the ticket was created and that was all. End of August they debited their amount from my account and I reversed it that's when they started calling me and closed or stopped the account with them. To my surprise they said I owe them, and they've been calling me for that. I had to dispute their debit to get attention from them. End of September they've increased their money owed by me to them as if it's another month installment. I really don't understand why would they treat their customers like that.