Booking.com complaint: Taking time to get refund for the air tickets

I booked 2 air tickets for my parents with booking.com on 15 of July 2023 and using my master card. I received ation emails from booking.com for the trip and the trip is on 16 of July 2023. On 16th July, I had check with airline application for my parents and it shown my booking was cancelled because of didn’t get air tickets fare from booking.com. That is why I called customer service and told about that. They said yes your booking is uned but we don’t know why and we will check airline but I didn’t get any reply. I had bought air tickets again from other agent for my parents on that day because that airline only flight twice a week.
I called many times to customer service and many message from my booking.com add but they only said they will check with airline. On 4th of August, 2023, I received two emails from booking.com and go to gate which is partnership with booking.com and said that they have received full refund approval from the airline and the booking have cancelled so they will start the refund procedure. They said they will make full refund in the same mode of payment as soon as possible but today 27th of August, I didn’t get any refund yet. I called to customer service many times but they said we will check with airline even though I told them I received email for refund. I sent messages in application but nothing happened.
The airline is Myanmar National Airline
Date: 16th July 2023
Trip: Chiang Mai, Thailand to Yangon, Myanmar
Customer reference 40-390197252
Pin code: 6119