Unless you purchased insurance, why do you believe that your Dr.'s note entitles you to a free change?

Unfortunately, you get a double hit here... the change fee and the current pricing on the route. When you change any non-refundable ticket, you are subject not only to the change fee but the difference in price between what you paid (mistake fare?) and the current fare.

Good luck on getting any where on this one, especially since you are dealing with cheaptickets. They are good for cheap tickets where you fly as planned, but purposely challenged when dealing with changes.