@Kyoung ****
sadly, with what you shared with your application, you were doomed for failure with your seeking a DTV Visa for medical care.
IF you are planning to try the Muay Thai training route to get the DTV visa,.be sure to use a Muay Thai training gym that has been successful in getting the DTV visa for its students.
There are several fine gyms that have been successful in getting over a thousand students approved.
Carefully Read the posts about getting the Muay Thai DTV on this forum. Choose the gym wisely.
Where are you going to live in Thailand ?