I followed your instructions and created a new user in this company with administrator privileges. After I logged in with this account, I could also see the email address of my old account under the menu item "Users". Then I deleted my old account, which after that was no longer visible in the menu item "Users". But I still can't be invited by another user.
Furthermore, it is still possible that I can log in to RMS with my old account, although it should be deleted.