New user, can sign in but can't finish setting up internet plan

I'm trying to set up Xfinity internet at my new residence. I created an Xfinity ID and chose a plan, but didn't finish (had to go double-check that I had entered the correct address for my new place). When I signed back in later to finish, I was not able to manage my plan, access my account settings, or anything. After signing in, most pages around the Xfinity website either don't finish loading at all, or give me an error:

"Something unexpected happened.
Try refreshing the page. If the problem persists, please check back later."

This has been going on for the last couple days. I've tried two different browsers (Chrome and Firefox), I've tried private/incognito windows, and I've tried clearing my cache/history/cookies.

I also tried using the mobile app, and when I signed in to the app, I got an error message:
"Access not Authorized

You signed in successfully, but you must be an Xfinity user to enjoy this service."

How can I finish activating my plan so I can set up my home internet?