Be careful not to confuse the terms -- Refund and credit/FFC. They are not the same things and operate differently. It sounds in your case the right term is credit / Future Flight Credit.
Also best not to use the "stole", purchasing air travel can be confusing and there are many rules but you need to have a full understand of the situation.

Need to know more about your ticket. Was it Basic Economy, most most discount ticket. It is not eligible directly for FFC -- it is the cheapest but is not changeable. However for a fee it can be converted to a changeable ticket. So specifically ask about Basic Economy.
United's Basic Economy - Discussion, Q&A, ...Now cancellable for a fee

Also Asia has non-changeable ticket -- this is stated at time of purchase, Is this the situation?
https://www.flyertalk.com/forum/unit...tinations.html

Anything more you can tell us about your ticket?
Where was it purchased?
When?

As UA does not fly to BKK,what was your routing and what airlines are involved?