Didn’t you already talk to ATT and they confirmed you didn’t owe them any money?
Was the cell phone # in question in someone elses name? If its not in your name I don’t think they can come at you for debt collection.
You could look at your credit report and make sure tehre is nothing there thats unusual. But unless ATT or a debt collector comes after you then I don’t see a reason to file complaints against ATT if ATT says you don’t owe them. What would the complaint be against ATT?
Well I got the dreaded letter in the snail mail today. A Disconnection Notice for my telephone service!
That caused me to jump start my inquiry with AT&T. I called the number listed on the notice. Problem with that number is it’s an answering service and I refused to cooperate until I finally got a real person.
After talking to 2 people and getting no where I finally got a supervisor. I’m a long time customer and I have auto pay which shows my landline telephone bill is paid though February.
I told him I disputed the Citibank bill as fraud or a scam because I have AT&T autopay. Finally he figured out that this was their mistake.
His attitude changed promptly and he was very apologetic. Now just think of all the turmoil this has caused me to go through? Should I make a claim? 
So its actually just a ATT clerical error?
Now I’m confused.