Yep, it's a legitimate offer.
I've asked a Comcast employee to help you. You should expect a reply in this thread.
I can check to see if I have this offer available on my end. To protect the privacy of your account, please send me a private message verifying your first and last name, street address including city state and zip code, and the full account number or phone number associated with your services.
To send a private message click on my name "ComcastChe", then click private message me.