I had the same thing happen on a flight to Paraguay. I initiated a Chargeback with my credit card company and received a credit in just a few days. The dispute is not settled yet but the airline must demonstrate to the credit card company that the charge is legitimate. With the flight cancelled, they cannot show the validity of the charge so the credit on the account will stand. This seemed to be the most prudent way to get a refund with foreign airlines like Aviana and LATAM, especially with the Chapter 11 conditions. Good luck!