Unable to use my Apple Gift Card says its not activated for use

Please follow the steps in this Apple Support article. 

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

If after reviewing the article, and following the directions in the article, you need additional assistance please follow the link below to contact official Apple Support. 

Contact Apple Gift Card Support

If you receive a request for payment using Apple Cash, or If you believe you are the victim of a scam, please contact Apple Support and report it to local law enforcement.

You may also report the scam to the FTC Complaint Assistant.

Use this link for issues with your Gift Card:

If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support

If it says it has not been activated, then that is something that has to be done at the store where you purchased it and there is likely nothing Apple will be able to do. It may be best to take your receipt and the card back to the store to find out why they did not activate it when it was purchased.