Can't find Blizzard account


Why is it that after every time i try to log in to Blizzard account to play Diablo 3 in a different place, it says that it can’t find my account… and i can only log on again when i change my passwords. I have mobile authenticator too, but it doesn’t even offer the possibility to verify my account that way. It is annoying and stupid. I play Diablo at home and sometimes at work too when i have time, and every time i play it at work, it logs me out from account and that problem happens. E-mail and password are absolutely surely right. Thank you in advance for any reply