We'd love to help you reconnect back to the network! There are several troubleshooting options we'd like for you to try. The first one involves resetting your network settings, which will be the seventh step on this page. This options resets Wi-Fi networks and passwords, cellular settings, and VPN/APN settings. Be sure to document/save your passwords before doing this.
You can also use our Troubleshoot & Resolve tool as well. You'll need to select your device to begin. Once you've done that, you can select Phone calls or Messaging beneath Service/network issues. We look forward to hearing back from you!
Collin, AT&T Community Specialist
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*I am an AT&T employee, and the postings on this site are my own and don't necessarily represent AT&T's position, strategies or opinions.
I have a SAMSUNG international 4G phone and an AT&T connection. This was working fine before the PIE 9 update. Since the update my mobile data stopped working. I tried everything, changing the APN settings, toggling, talking to SAMSUNG India and US to no avail.
Here is what was wrong: It seems like AT&T has 3G and 4G/LTE sims this problem is with their 3G sim it doesnt work with the new update unless you roll back to 3G APN settings. So the solution instead of doing all this is just to go to the AT&T store and ask them to try your phone with another display 4G sim. It will surely solve your problem.