i paid off our galaxy s9 and s9+ early in order to have it unlocked for our trip to mexico. we just got here last night and i purchesed a couple att sim cards (sim trio voLET r) in the airport. i rebooted my phone a couple times already, but when i put the att sim in it prompts me for the unlock code and the one given to me does not work. i tried getting support via text (from mexico, so i hope they credit me back for those texts!) and they only thing they could suggest was to try a different carrier's sim card.. i've already been seriously considering switching carriers now that my phones are paid off due to several issues, including not having the option to opt out of the automatic credit card bill payment and the fact that comcast charged my credit card almost $1000 in error when i had to have it replaced under warranty, and they sent me zero communication advising me of the charge. i just happened to notice it on my cc bill. and when i tried to get answers from a comcast manager i was told he would investigate and call me back. never got a call back.
They should have given you 2 codes... the 1st is the unlock code which never seems to work, the 2nd is the unfreeze code. That's the one that usually works with Samsung. Keep calling till they give that to you and don't enter the one you have anymore or you will lock yourself out.