Comcast website doesn't allow all valid email addresses as usernames

To log into the Comcast website, you need to create a username which must be a valid email address. Unfortunately, the website doesn't allow certain characters which are valid in email addresses (according to RFC 5322). So I have to enter a valid email address, but I can't enter *my* email address because it has characters that Comcast doesn't like (specifically, the "+" character).

I sent email to Comcast but received a canned response about what a username is (I honestly would have rather gotten no reply than a reply that proves that my email wasn't actually read).

I wasn't really expecting an email customer support rep to fix the website but I would like to hear that this issue has been escalated to the people in charge of creating the website so they can consider fixing it.