Apple gift card already redeemed, what to do?

Check the information here, If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support Did you purchase this gift card at a retail store, such as a grocery or box store like Walmart? It may have been activated incorrectly, or someone added it to their device at the store and left it there. People will do that sometimes and steal information from the cards at the stores.

▷ Check gift card balance. 

I purchased an Apple Gift Card yesterday and when I tried to use is last night it showed it had already been used. Is there anything I can do not to lose this $100.

Check the link provided in my earlier post.