Even if you have a proof of purchase, they will not refund your money.
You can report it to the police.
. . . This goes for all gift cards at all stores.
Depending on what you mean by Stores.
Where to buy a physical Apple Gift Card or App Store & iTunes gift card: at an Apple Store or an Apple Authorized Reseller in your region.
If you have a valid payment method on file, instead of buying or order an App Store & iTunes gift card, you can Add money to your Apple Account balance anytime, no gift card needed, see -> Apple Gift Card - Apple (UK)
See -> If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card
If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support
See also -> About Gift Card Scams -> About Gift Card Scams - Official Apple Support
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Tips to avoid becoming the victim of a scam
- If you are NOT purchasing an item from Apple — such as from the Apple Store, iTunes Store, App Store, Apple Books, or for an Apple Music subscription or iCloud storage — do NOT make a payment with an Apple Gift Card, App Store & iTunes Gift Card, or Apple Store Gift Card. There's no other instance in which you'll be asked to make a payment with either of these gift cards.
- Do not provide the numbers on the back of the gift card to anyone that you don't know.
- Immediately report potential scams to your local police department as well as the FTC (reportfraud.ftc.gov).
Contact Apple
If you have additional questions, or if you've been a victim of a scam involving Apple Gift Cards, App Store & iTunes Gift Cards or Apple Store Gift Cards, you can call Apple at 800-275-2273 (U.S.) and say "gift cards" when prompted, or contact Apple Support online.