This has been very frustrating. I turned the data off of my husband's line when we traveled to Europe. I've turned it back on through att.com and spoke with customer service yesterday to tell them that his data still isn't working on his phone. She said she took the "data blocker" off of his line. Still no ability to access data. Went to the Microsoft store where we bought his phone, and they verified that his data is on in the settings.
Not sure what else to do, but am seriously thinking of switching back to TMobile since I've had lots of frustrations with AT&T in the few months we've been with them - mainly with customer service not being able to help and/or being somewhat rude. In over a decade at TMobile I didn't have this many issues and am thinking I made a mistake by switching. 