how to get full version games

I'm not sure I understand what you are asking. Did you download a demo version of a game? Did you get it from the game's developers site? Are you using the App Store? You haven't given us enough information in order for us to help you out.

FIrst i download a demo then for level 3 that game ask to buy a full version. I purchase by credit card and done. after that i'm back to play then i click already paid so i can't play. what a wrong about that?

SO what can i do tet the full version?