Have you contacted the airline directly to verify if a refund was issued?

If you paid for the ticket with money, I would dispute the charge. If you paid with points, I would file a CFPB complaint. https://www.consumerfinance.gov/complaint/ .The fact that Chase changed service providers is irrelevant. If, in fact, the airline has not issued a refund that could be relevant, but it seems just as likely that they simply don't recognize that it has been received.