Please see https://www.xfinity.com/support/articles/updating-your-mailing-address. You can't change this yourself, you need to have a Comcast rep make the change for you. If an Employee doesn't reply to your message here contact a phone rep at 1-800-Comcast, or see https://www.xfinity.com/support/contact-us to chat or schedule a callback.
I wanted to touch base and make sure you were able to make the change to your billing address. If not, Can you please private message me your full name? Thank you for posting to our forums.
To send a private message, please click my name "ComcastMartin" then select "Send a Message" on the right side.
I know it has been a while since you reached out but I still wanted to double check! 🙂