I recently bought a S8+ and found out that its an unlocked international phone with 2 IMEI's. The guy i got it from said it would work with any carrier and he put his sim card in from T-Mobile and it worked. I got it home and went to my carrier(AT&T) outlet store and they tried to get it working with AT&T for over an hour and it kept showing no network at all. Is there a way of getting this international S8+ to work with my carrier AT&T?