Maintenance page when logging in - This is the fix
Site:
If you have Google Chrome, click on the Chrome settings tab (three horizontal lines in the toolbar), then select "Settings", then at the bottom of "Settings", click on "Show Advanced Settings...". At the bottom of "Advanced Settings", there's a "Reset Browser Settings" tab. Click on that and then "Reset" in the box that appears next. Once completed, you should be able to log in to ATT.COM to pay your bill. This worked for me. Not sure what to do if you do not have Chrome, but try resetting your browser.