Keep dividing with no service

Installed an alarm system not working. Sent the quality control guy and he agreed. Been calling adt and they've only escalated the matter so many times. Finally come back to me and say I need to pay an additional 3000 ontop of the new alarm system to work. My hands are tied so I agree and ask them what happens to all the months they've been debiting my account with no service and they say they they will give me a credit. I asked them to put it on a letter head and in writing and its 2 days I'm waiting for a simple letter.