It's unclear from your post when you actually first called KL to try to fix this? You were scheduled to fly on Saturday and were released on Saturday. At what time was your flight and at what time were you first able to access a telephone?

Generally speaking, it sounds as though you had a discounted & restricted ticket which has little or no value if not changed/cancelled before the first flight. This is what your travel insurance is for, just as it would be used for any other expenses related to your medical episode.

How would KL know that you were sick?