> I'm sorry that we have been unable to resolve this issue. If {demand for refunded amount} is not processed by {date one week from now} I will begin the chargeback process with my credit card issuer {bankname} as I did not receive what I paid for. Please keep me updated if anything changes.
This puts the pinch on both the vendor that processed the transaction (since they're going to be the ones getting their merchant account dinged, and since they're going to lose whatever money was charged to the card + a fee for the chargeback) and the party ultimately responsible (wanna bet that AirBnB isn't going to be happy with your host for causing them to lose several hundred dollars on a transaction they only stood to gain $54 from in the first place?) Things should get resolved pretty quickly once you step outside of the box & assert whatever rights you have under your credit card agreement.
I've had to do this with Agoda over a reservation made in Thailand. And I used to sell stuff on Ebay - no one pulled this on me, but I know firsthand how much companies like PayPal hate it when their merchants get chargebacks.