My gift card already been redeem but not by me
I went to check my balance on my gift card and it said it’s already been redeem
Question marked as
See If you can't redeem your Apple Gift Card or App Store & iTunes Gift Card - Apple Support
Note that simply "checking" the balance will redeem the entire value of the card. There is no way to "check" the balance. It's either the full value or nothing because it was "checked".