I booked foy my parents 2 one way tickets from Koh Samui to Bangkok on the 20th march. However they wanted to change the travel date to the 19th of February. So I called Thai Hotline, which told me

1. It is not possible to change the date of the flight to an earlier one.

2. It cannot be done over the phone, but has to be done in Thailand at the airport.

3. The change fee will be 500 baht per person

Are these information correct? It seems a little strange for me. Normally when I have a flexible ticket I can also switch to earlier dates, and I have also never heard that it has to be done at the airport.

Furthermore am I believing that Thai will cancel the old ticket for 500 baht, which means that they would have to buy new ones. Will they just use this amount to pay for the new ticket or will they refund it to me ( I dont have the credit card anymore, which I used to book the ticket with)?

Thank you already for your help.