Hello JahgDohg!
Looking here at the path you described (Settings>Cellular Data>View Account) this is something used, in my experience, with prepaid accounts. Without being able to see your specific account type I could not say for sure, if you have a postpaid (contracted) account you would manage your services for this iPad right on att.com
AT&T Login Page
If you have a prepaid account you would be able to access your account using that path or by going to the prepaid site online
AT&T Ipad Landing
If in your situation you have a prepaid account and those internal settings don't work for you you can try the link above or contact AT&T for further troubleshooting on how to get that workingImage may be NSFW.
Clik here to view.
They have a chat and a number to call in for support -- 800 331 0500.