Well, AirBnB told you wrong. In fact, their service team is either poorly trained or just outright lying to get you off the phone/chat. Apple is not a bank and is not involved the refund process. When you initiated the return with Airbnb the process goes as follows.
Airbnb approves the refund and instructs their credit card processor to refund the money. The credit card processor refunds fees they were charging and withdraws funds from Airbnb’s bank account. Funds are then sent to bank that issued your payment method (credit or debit card) and bank credits your account the refunded amount.
Credit card refunds are tracked via the Acquirer Reference Number (ARN). You need to ask Airbnb for the refund ARN and then give that number to your bank so they can track the refund.
Happy to answer any questions, but Apple is not involved in the refund process, does not have access to ARN and is not connected to the refund network. So, even if Apple had the ARN, there’s nothing they could do with it.