Terrible customer service

I cancelled my ADT contract last year due to contract breach from ADT (jot responding to my panic button, which i pressed 3 times, their excuse, they dont have enough vehicles. After months of fighting with them, i finnaly got a letter, confirming my cancellation and that my account is paid in full, but today I receive a message that my account is in arreers. I am so frustrated and i truly hope nobody falls into the same trap we did. Do not trust Adt, they dont commit to their promises and they have now damaged my credit record as well.