Here’s an idea:
Pick a time that is convienent for you to go to the doctor. Send them a card confirming an appointment at that time. (The doctors do this to me all the time.) Note on the card to call you if the appointment needs to be changed. Mail the card to the doc and don’t forgedt to show up at the appointed time.
-or-
Do like McKenna and just show up. Get really irate that they gave your appointment to someone else and demand that they see you as you had to rearrange you entire schedule and hired a sitter to accomodate them.
Let us know what happens. 