Just a thought: have a look at the network messages in the browser when the password is reported to be wrong. Maybe that would give some clues as to what is going on? There may be some JSON bodies you can look at.
Maybe the account is associated with an auth provider, and thus rejecting a plain password auth is correct?
(Since this is an account-level issue, emailing billing@ was the correct thing to do, per the help docs. I would not recommend sending multiple messages though; that just gums up the support channels for everyone.)
Support repply me thx
Solved! Turns out the login system is case-sensitive, and the email was registered with different casing than what I was typing at login. Using the exact casing from registration fixed it.