@cocoa One thing you could try, if you haven’t already, is this:
Read and follow this Support Guide → https://answers.netlify.com/t/support-guide-help-i-cant-login-to-my-netlify-account/119360
It’s how you would traditionally raise issues with creating an account.
I’d mention that you’re concerned the email address might be be blocked on their end.
(Since they communicate to those tickets via email - so if it is, you may not even hear back.)
I suspect if it had been blocked, they’d have mentioned/fixed it though, when they provided the bounce info.