1. Sounds familiar to what I have seen in China.
2.The money not paid to you was no doubt divied up among the administrators concerned. Nice bit of pocket money.
3. I don't know why you let them treat you that way. That is being passive. Yes I also blame the victem. You expect Western manners? Why? Play tough. These are crooks. Before you left you could have packed the computer or the main internal micropanel at least), but not before telling them that it was fair compensation, in lieu of cash. Sometimes that loosens the purse strings. Project strength, not wounds.
4. You could have added that you would be circulating the theft of salary in a Chinese written statement to all students. Photocopiers are wonderful for pamphleting. That's micro-politics. I would have gone to the police with a translator and reported the theft. You can still give that a try.
5. Sounds like the many crooked schools and universities in Korea. Had my fill of them.