If you check your email with Comcast's Xfinity Connect webmail ( https://connect.xfinity.com/ ), look for the XFINITY Verified Email logo next to any message that claims to be from Comcast/Xfinity. See https://www.xfinity.com/support/articles/comcast-verified-email.
Can't say for sure without more information, but it sounds like a phishing email, a scammer attempt to steal login and account information. If you want to report this to Comcast see the "Report Spam and Phishing Emails" link on https://internetsecurity.xfinity.com/help/report-abuse/. Scroll down to the "Report Phishing Emails" section.