We got one as well. It went into the shredder!
I got that number directly from Anthem-BlueCross and it is GOOD. I spoke to them on that phone number. The website is also good for signing up for two years of ID protection if you are or have been a BlueCross or BlueShield member in the past ten years. The lady at the phone number highly recommended using the website for signing up. . . and doing so if you were a member of their insurance companies. The likelyhood of your data being compromised was quite high.
Anthem-BlueCross and Blue Shield have sent out press releases about FAKE EMAILS warning about the breach with phone numbers to call to sign-up for id protection that are them selves phishing expeditions! They are warning to NOT call the numbers on those emails, or click on any links on those emails. SHEESH!
These fraudsters will take every opportunity to steal your ID.