Mastercard complaint: Disputed charge by Frontier Airlines

For almost a year my wife and I have been disputing a charge by Frontier Airlines for flights out of Buffalo to Florida. Frontier claims we were no shows and we didn’t cancel our flight even though we called them beforehand to cancel but they wouldn’t cancel and give us a refund.
This was back in March 2020 when the borders were closing between Canada and the US so it was tentative if we would be able to drive to Buffalo from Ontario to make the flight let alone get back into Canada if we did go to the US. We called frontier after the fact and they offered us a useless 3 month voucher so we talked with MasterCard to dispute the charges. Initially the credited us the full amount while they investigated and said that the merchaint had 40 days to respond to master card and it to almost 90, then MasterCard re-debited us the full amount siting Frontiers position that we didn’t cancel and we no shows. My wife faxed the email conversations between her and Frontier over to the investigation department at MasterCard and we were told THREE TIMES over the next number of months that we would hear back from them directly which we never did. We called mastercsrd again to question what is going on and they told us there is nothing they can do for us and to file a complaint instead.