I don't even play WoW anymore, I used too, but I don't.
Thats why im suspicious.
If you didn't sign up for the annual pass, chances are extremely low that you got invited, but I had heard of a few opt-ins getting it.
There are some phishing scams disguised as Beta invites, log in to your battle.net account through the official site, if you did get the beta it would be in their.
all it does it take away time from grinding on your released version.
Any progress you make on your beta server character doesn't transfer back to the live server.