@Merinnnnn
For the error your receiving if it says it's already used it's normally pretty accurate. I'm not sure if the person who a gave it to you used it themselves or got it from someone else who did.
You would still this point need to call customer service and provide them the code and they should be able to look up whether it was used. Normally 30 time codes comes when you purchase the game directly from like origin or Amazon bubdle. The 60 day codes are ones that are purchased separately along with 90 and 180 time codes.
Either way I would call to verify the code. See db woodynz post here with a link to numbers and how to use skype if you have it.
Using skype with that contact is a free call to the best of my knowledge, that number is only available as per the hours listed (Support available from 9.00 CT - 21.00 CT) so need to confirm time zone etc