I just recently bought Crysis 3 (PC), on coming home, I turned on my computer, installed Origin, and tried... tried to register my game. On attempt it said. "This code has already been used." Now, I'm not a rich man, and I can't really afford another game if something like this goes wrong. Please help at the earliest convenience.

Contacting support is your best bet

You may want to contact the store from where you have bought the game and provide them not just the information, but a picture too. They will likely give you another product. If the store won't help you out, try EA's support.