I personally never had a problem with SK (perhaps status helps?). I would definitely not bother with the legal case on such minor issues, but would just call them again. In the worst case in my history of dozens of refunds with SK, I had to call twice, to get that through. It is actually the best airline I know when it comes to refunds. Even in these messy times, they were the fastest of the three airlines I had open claims with. The slowest so far is Lufthansa, with no progress whatsoever. You might prefer the legal way - good luck. Out of pragmatism, I recommend calling once again to figure out where the thing got stuck.