suddenly I cannot connect to Xfinity email POP email (authentication failure)

About 2 days ago, my Thunderbird client cannot connect to the Xfinity email account I have used for years with no change. It tells me authentication failure.

So then i try to log in to xfinity webmail and it demands that I change my password. But I cannot receive a confirmation via email because that is not working. I also never set a mobile phone number on the account, instead the phone number on the account is a land line, so i cannot receive a confirmation via text either.

When I try to sign in to xfinity chat, i have the same problem: it demands I reset my password. But that can't happen! It's a big catch-22!

What else can I try?