I redeemed a live gold card i bought from the store and it does not work,

What error did you get, if any?

Hello, I read your question, and I believe I understand your position. The Xbox Ambassadors are here to help.

After reading your post, I have a few questions. May I ask did you buy the code new, or from a trusted retailer? Also, when you say it doesn't work, what specifically does not work about it? Was there a fault code? Or any other prompted screen? Have you
tried power cycling your Xbox or attempted to play an online multiplayer game? Let's begin to troubleshoot your situation.

You need to contact support

https://beta.support.xbox.com/contact-us

As someone else said, I would reach out to support. That said, did you at least check account.microsoft.com to see if Gold shows up in your subscriptions?

Did you get a message when you redeemed the code, like did it confirm that it was successfully added to your account?