I get these fake Diablo e-mails quite often. I know they're fake because I don't play Diablo, #1. I also look at the TO e-mail address to make sure it's my correct address, #2. Because I know who I have accounts with #1 usually is a dead giveaway it's a fake.
If you have any doubts whether something is from a company you do business with, open your browser, not through the e-mail, but the regular way you'd open your browser and go to that site. Look for a phone number or some way to contact them; I usually like to find a phone number since I like to speak to a live body.
Contact that company how it's specified and explain the situation. The ones I've called were more than happy to listen to my situation and in ALL cases assured me what I'd received was fake. They also took the time to give me their fraud department e-mail address so I could forward the fakes to them.
If something gets your goat, it just proves you have a goat to get.