Gift card empty

Had a gift card with receipt for amount that should be on card. Went to redeem the card on Friday with a purchase. They told me the card was empty. Asked them to look into it as I am confident I hadn’t used the card. Told me they can’t trace what was bought with the card? Also said they will look into it and give me a call back 1 day later. I haven’t received any feedback or phone call regarding the matter.