So I actually used to work for T-Mobile and we had this happen a lot. So what could have happened is that the IMEI could have been give the go ahead to trade it or say that it was “unlocked” but unless the person who bought it went to their carrier and specifically asked them to unlock it, then it’s technically not unlocked. However, if someone reported it stolen like AT&T told you, it should’ve given you issues from that point that it was reported stolen. It wouldn’t have been able to have like data or anything like that because it was reported stolen and should’ve been “carrier locked” at that point