Code not activating on origin, says key is used already

Usually games that are bought via Origin will be redeemed on your account automatically after purchase. Although you will receive a mail with the product code, this code is most likely already tied to your account. So, if you are told that the code has already been used, please check your My Games tab first and if the game is not shown there, then please contact a Game Advisor at https://help.ea.com/contact-us for further assistance.

Since you purchased it elsewhere, you'll probably have to contact a Game Advisor & let them sort it out 🙂

Since this is a public forum we cannot help you since it would involve accessing your account which we cannot do.  In order to solve your problem you will need to speak with at game advisor at EA Customer support:  https://help.ea.com/contact-us

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.