Please help me refund the plastic surgery reservation fee.

Reservation confirmed for 5/24 (Fri) surgery date 6/11 (Tue) (reservation fee 170,000 won)
 Contents stated in KakaoTalk: 100% refund if canceled within 4 days
 As a precaution, the hospital extended vacation (~6/8) It says that if you want to cancel, please contact us in advance by May 31st (Friday), but
 I didn't see the details. I made a cancellation inquiry on June 4th (Tuesday), but couldn't contact you due to vacation.
 
As of June 4th, we canceled a week before, so 100% refund. However, I was contacted today (6/10), the day of return from vacation, and was told that since the surgery was tomorrow, it would be considered canceled a day before and only a 20% refund would be issued. Instead, they say they can put the surgery on hold and postpone the date.
 
The refund policy states that you should get a 100% refund, but in exceptional cases like this due to vacation,
 you should have carefully decided whether or not you can reasonably get a full refund... I'm so stressed out. Is this a battle where I'm at a disadvantage?