havent received my refund for deposit

I had a keyboard that was accidentally sent to me as a replacement and Apple took $100 as a deposit until I returned it. I sent it back and have received notification that it was received, but I haven’t received a refund yet and it’s been 3 weeks since they received. They took the money immediately, yet they aren’t refunding it. It has been impossible to send them an email or chat with someone online. Any ideas?