You couldn’t have had two accounts linked to the same email...or maybe you meant to say one account with two nickname/username aliases. In the past, it was possible to have one account with two different identifiers:
However, this setup has been gradually phased out (likely by region / by interface). For example, on one of my accounts the switch happened earlier, while on another I could still use the username to log in until recently.
Now (or at least in the process of being rolled out), the system syncs the community identity and login credentials directly to the email associated with the account, rather than to the username. This makes the login more consistent and unique across all platforms whether you’re accessing the community forum, ACC, account management, or software products such as Revit, AutoCAD, or Navisworks.
Bottom Line is do not Panic 🙂 simply set windows to remember you (the email used to log in not the password) and you should be good to go