Double check your UserIDs on your home system with the Lookup tool at https://idm.xfinity.com/myaccount/lookup. After you enter the requested information you'll see a list of the UserIDs on your account and an indication of which one is Primary. Be aware that the Primary UserID online doesn't always correspond with a name on your billing statement.
If the ID you are using is not Primary, you'll need to log in with the Primary ID. If you need help with that, or if your ID is Primary but you still don't have access, contact one of their reps at the phone number on your bill or 1-800-Comcast, or use one of the other options on https://www.xfinity.com/support/contact-us/ and have them fix the problem.