Incorrect billing

I installed the alarm system with ADT in June 2012 and it was ending after three years and i am now on a month to month with them. To mean that means that i own the alarm system and i should only be billed for the arm response but i still pay over R400 while i own the device and they only responsible alarm system.<br> When my battery was finished they refused to replace it because i am not on a month to month but they are glad to take my R400. That's an ************ business practice. i want to be billed strictly for arm response not the device.