Sent wrong version of book as gift

I sent my dad a book on iBooks as a gift when I meant to send the audiobook version. I can’t seem to find a way to get my money back so I can send him the correct version. I can’t get a refund through reportaproblem.apple.com because the charge is still pending (I’m assuming it will stay this way unless he accepts the gift). Does anyone know how I can correct this mistake? Or a way to contact apple? I can’t find any solution or a way to talk to customer service.