If I am following the chain of events correctly, it looks like when you make the change the second time, they may have reissued the ticket as non-refundable, as the receipt indicates? While it's great they noted all facts in the notes section (allegedly), they should have reissued the tickets with the proper fare basis that allows changes with no fees.

With that said, I was also under the impression that tickets purchased with residual credit from non-refundable fares would render the new ticket non-refundable as well, regardless of fare basis.

Lastly, with medical-related issues, you should also pursue the medical waiver route to reduce the change fee from $150/200 to $50. Just need a note from the doctor.