They're not obligated to provide you supplemental insurance, nor an explanation why they reject you. The ombudsman can't help you in this regard. If you really want to know why you didn't get the insurance, better ask SWICA directly.

It is speculated that some insurers factor in the residence permit on their decision, but this is only hearsay. Maybe Jenny or somebody else can give you more details, if the permit or specific pre-existing conditions are important factors.