I send $700 Apple store gift card to a buy with my receipt and he said my card is used

Hi Apple support please I need your help on my cards cause something really bad is going on right now which you are the only one that can help me out with this .. I send $700 Apple store gift card to a buy with my receipt and he said my card is used and I know this is not truth and is trying to rip me . But I need your help urgently on this with the time and date the cards was been redeemed . Pls will be waiting for your reply ASAP .

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