Sent second gift card by mistake
I sent a gift card to niece but in not seeing a response from iTunes “as sent” I repeated the process thinking I did it wrong the first time. Later that day I found two receipts for gift cards in my email.
Gift apps, music, movies, and more from Apple
https://support.apple.com/en-us/HT201783#cancel
Cancel a gift
If you want to cancel a gift, you can contact Apple Support [ http://www.apple.com/support/contact/ ] up to two days before scheduled delivery.
If you still have questions or problems:
Contact Apple. Click here --> https://support.apple.com/choose-country-region Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service --> "See a list of Apple phone numbers around the world."
Click here --> https://support.apple.com/HT201232