When I try to login in to my Bitbucket account account through Bitbucket.org in a web browser, I get the message "Your email address already belongs to a Bitbucket account. Please log in below.". Logging in to Atlassian.com works. I've tried different web browsers, but it won't work. I'm still able to use SourceTree and Git.
Logging in works again.
Sounds like you are on a signup page rather than a login page. What is the URL of the page that you're trying to log in to?
https://bitbucket.org/account/signin/
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