No account access in Europe

I opened a new account last month and I set up a user ID and password while home.  I’m traveling in Europe now and cannot access the account to pay my bill.  When I try to recover my ID and/or password using my email it says, no such email exists in our system and yet I receive emails from AT&T.  How can I solve this and pay my bill?  I tried downloading the app but that doesn’t work either.