As for your issue, the "code used" message means the code is already registered to an Origin account. There can be number of reasons for this.
Did you purchase the disc online? Used? The game code is only redeemed once. After it has been registered to an Origin account, it becomes used.
Did you enter the code and nothing happened, then reenter it? This can be common for DVD installs. If that's the case, the code has been registered and you have to wait for the game to be activated (the game entry shows up in your My Games library) before the install will continue.
If none of the above, you'll have to contact a game advisor (accounts) via live chat from your computer to check the status of your account and where the game code may be registered.
Origin client Menu:
Help > Origin Help.
Live Chat link, up top next to the Search box.
or here..
1 Click on the following link: https://help.ea.com/contact-us
2 Make sure you are logged in (top right corner)
3 Click on the blue button "Contact a Game Advisor"
4 Enter the name of your game or product (or "Origin" for account-related issues) and click "Find Solutions"
5 Select the type of issue and the platform you play on, and click on "Find Solutions".
6 Click on the blue button "I still need help" if the FAQ articles do not apply to your situation.
7 Select a contact option. Note that you may get different contact options depending on your country.
