The most common reason we see this happening is when someone logs in with Facebook initially, then uses email/username/password to create an account.
In our system, those are actually two separate accounts, even if your Facebook account is linked to that same email address you use to create the second account.
This same scenario can happen in reverse as well, if you initially create an account with email/username/password then log in later with your Facebook account.
Before reaching out, try logging out of the app, then logging back in using whichever method you created your first account with!
If that doesn't work, then feel free to reach out and we can help you out!