Anonymous participant - You can’t apply via Hanoi if you are in DaNang. The embassy has a list of which provinces are allowed to use which embassy. DaNang is assigned to HCMC. This could be the problem.
Anonymous participant - it sounds like you did it correctly. Any hyphens or other symbols in your name? Did you enter your info or leave it to the application to pull from your bio page upload? The site is known to incorrectly pull info from your bio page, so needs to be rewritten after it is uploaded. For example, the letter o might be replaced with a zero, etc.
They stated it was because of wrong personal info? If your middle name is on your passport, you should include it, regardless if it is/isn’t on other documents. What did you state as place of passport issued?
Anonymous participant - Not sure if they can tell if it is refundable or not. The bigger issue is if they want to see your flight from Thailand to UK, which would have to take place before you applied and if they want to see your passport pages. Once you have the visa, you will need to leave and re-enter anyway, so why not just leave and not risk doing something technically falsely