Two Apple gift cards redeemed into someone else's account the day they were bought
Two Apple gift cards. The first time the recipient entered one, the system said it was already redeemed. Apple could see the redeem happened the day of purchase. What Apple could do was mark that account as fraud. The refund still goes back to the store that sold the cards. Marking the account as fraud does not turn the money back into a new gift card.
This is separate from a sleeve and a card that do not match. Here the gift card had already been redeemed into another account on the day of purchase. Who can see where money was spent is in who can see where it was spent.
A new phone, and the same Apple gift card says already redeemed
The gift card was used on the first phone. The second phone should not take the same gift card again. The message is already redeemed, and the balance is still in the account that redeemed it. Check whether the account you are signed in to now is that account. A different phone does not turn an already redeemed gift card into a new one.
The Apple gift card in the email was already used when it was opened
There is no sleeve to inspect. The gift card arrived in an email, and the system said it had been redeemed. What remains is the sender: whether they redeemed it themselves, or whether the email was bought. There is no package to compare, and no activation line on a receipt to check.