I hooked it up in ITunes and did restore from backup.
Does it still indicate "activation required" when using any Micro SIM? As stated earlier in the thread, that means the iPhone has not been activated and needs to be activated via iTunes or via WiFi activation.
Since you purchased an AT&T version from Apple and if you paid full price then it is very easy to get the unlock completed. Go to the AT&T Unlock Portal and follow the instructions.
https://www.att.com/deviceunlock/#/
Many Apple and Carrier reps don't have a clue about how activation / unlocking really works.
Dave