If a person cancels their Thai Airways flight ticket within 24 hours of booking the flight, you get a full refund without any cancellation charges.
Thai airways cancellation policy says If a person cancels their flight ticket after a day, the person will be charged some chargeable amount and only a percentage of their ticket will be refunded.
If a person fails to cash the flight and does not even apply for a refund, the person will not get any amount as refund.