They may have just not gotten to your e-mail yet.
Open Stardock Central.
Click on Tools
Click on Register Products
Click on Games
If there is no e-mail there, enter one. I'm not sure whether it should be the one that you ordered the game with or the one that you made for your stardock.net account, but I would try the one that you ordered it with first. You can always edit your stardock.net account (it's another option under the tools menu).
Choose either TotalGaming.net (if that's what you ordered) or the individual games that you ordered from us from the pull down menu and enter your serial numbers there. You can copy and paste them right from the e-mail that you got from us.