Huh, my post vanished in the server hiccups it appears...
My recommendation was to have them call you. From their customer service help pages, one option they have is you give them a phone number and a time to call you and they will. Give phone number (if you want to be really paranoid, don't use your home number) and a time. When they call you, explain the situation and ask them for the phone number you are supposed to call to confirm your credit card information. If it matches what they told you in the e-mail, you can be reasonably confident that it is legit. If it isn't it is one heck of a scam.