Keeps on sending messages after account is closed

I had an adt account that was cancelled and 3 months after cancellation, they were still deducting money from my account. On the end of the day. they did refund of only one month. NOW, after a year I must find out that I still have an active account at adt and that it is in arrears. After numerous times that I have asked them not to contact me for an adt account because adt owes me that 2 months, they still bother me for outstanding moneys. Pls help these *********** fools...... People, STAY AWAY from adt and their counterpart canonies norman bisset & assosciates. They don't listen......