It seems to me that when you sign up here and order something, it is made clear that your orders/downloads/etc are tied to your e-mail address, which is your username. TGC clearly states this and warns about changing your username.
Quote: "I remember my serial number but i cant my username. Plz help.
"
Think about that for a moment. And how exactly would you like us to help. Please contact TGC, but I'm not sure that they can help you either.
The forum provides a means to hide our true identity. Too bad we always screw up and let it be seen.