Adt Security
Debiting big amount without permission

I cancelled adt due to poor service experience. I still had an outstanding amount and and agreed to pay it off.

I received a sms yesterday informing me that adt will be debiting my account of an amount outstanding. No amount stated in sms.

Even though I have an arangement with them, they deducted a huge amount of money out of my acount!

Since when can someone just randomly (on any date) take an amount out of your account without you agreeing to that amount or date. :(
I just don't understand!?