I assume you're talking about the phpMyAdmin tool -- as far as I'm aware, you have no user account enabling you to log on to "humbug" itself. You simply "connect" to your database; you do not log-on to the humbug machine. I assume, if you had phpMyAdmin installed on your own PC, you could do exactly the same by stipulating the database hostname as humbug.free-online.net.
The username is exactly the same as you use to log on to the portal, with no appendages -- ie <username>.
The password, is a completely different one from the one used for portal access, and will have been notified to you in an email sent to you as confirmation that MySQL activation has taken place.