Xbox Gift Card not working

My son brought an Xbox gift card from Walmart yesterday 9/18/2020. Once he was home, he scratched off the gray area for the numbers and and entered them in to redeem his card. He then received and error message stating the card had already been redeemed.
We called Walmart who referred us to this site. We are on day two now with no response from Microsoft. What do I need to do to either get his money back or receive the 25 dollars on his account.

:)