In addition to the support articles above, here’s a guide I made a while back that has some screenshots included.
Like the others mentioned, it wasn’t a real Bliz game master. Follow these tips to help spot whisper scams.
1) Watch for bad spelling, grammar and punctuation.
2) True GM’s will never link to websites for verification purposes.
3) True GM’s will have a special indicator that they are attempting to contact you in both the chat box and the upper right of the screen:
https://postimg.cc/image/824wp2bup7/
4) True convos with GM’s will open their own, separate, uniquely named chat window:
https://postimg.cc/image/7r6lfk4iyj/
5) True GM’s will have a unique, blue “Blizz” graphic preceding their character names and messages:
https://postimg.cc/image/8i5paf207v/
6) True GM’s have regular, self chosen character names, not “Game Master” or “Blizzard” or “Administrator”:
https://postimg.cc/image/3ut9jkr1gr/
7) You cannot report a true GM. If you right-click and the option to report is there, it’s a fake… so report it!