@janike0909 You can only enter the code once. If the code is accepted you can not re enter the code. Are you trying to enter the code in Origin? Does the pack show as owned in Origin? Open Origin - right click the game icon - click show game details - click extra content.
If you're talking about registering your game; than the code can only be used once; as said to the reply above.
Codes for just downloading the games can be used more than once. Registering your games isn't the same as downloading them.
If you bought the game already used, than the original owner could have used the code already; which will lead you to not being able to register it.
If it says that the code is already taken, it means it must have worked for you; or you've gotten a used code.
I hope I was helpful!
I do not work for EA.