Fine, my error, I'll pay the fee. I went to the AT&T online payment site and corrected the information immediately (around 11/5, when I received the billing information). My next payment wasn't scheduled until 11/17, so that shouldn't be an issue. You'd think, anyway.
Imagine my surprise when I got a mailed notification from AT&T last night saying my online payments had been canceled. (I actually don't know when the letter arrived, since no one's been home since last Wednesday.) I went to the site a few minutes ago to see what was up, and it showed my November bill as unpaid and past due. I double-checked the account information, and it's correct. So I tried to make a one-time payment, but the site wouldn't allow it because I'd had TWO returned checks within 6 months.
Naturally, the billing office closed at 7, so I'll have to wait until tomorrow to straighten this out.
tl;dr: I screw up an automated payment and pay the price, but then AT&T screws up a second one and holds me responsible, cutting me off from further automated payments.
(Oh, good. After typing all that, I thought to check for credit card payments. Done. Now I just have to fight the returned check fee and get my payment privileges restored. Sigh.)