After cancelling a mobile account in the middle of a billing period (which I later found out is not the best idea), I went round and round with AT&T customer service by phone. I was attempting to get a final, detailed bill. I would have preferred to simply log in to my online account and view the bill myself, but the agents told me it was not possible to reactivate my online account or to send a bill to my email address. It took 3 separate times on the phone to finally receive the correct, detailed bill at my permanent address. Waste of time and paper.
I still had questions about the bill, and, after waiting about 15 minutes on hold, customer service by phone was unhelpful.
I opened an AT&T chat window, and the agent was extremely helpful. She quickly sent a temporary password to the email address associated with my online account. I was able to sign in, view the bills, and pay in a matter of seconds.
I highly recommend using the online chat for any help with your account. Even if you have to initiate the chat by making selections that don't exactly match your issue, try the online chat FIRST. If you do as I did and use customer service by phone, be aware that you might be setting off an endless string of frustrating experiences.