A couple weeks ago, I was booking travel to a trade show and noticed the cheapest fare class was D. I looked at the seating charts and saw that the flight was heavily booked, so I guessed that so many people were flying-in to the city because of the show and went ahead and booked it, thinking that it would get more difficult as time went by.

Yesterday, I looked and found plenty of Z space and noticed that it would book at around $200- cheaper. I tried to use the change function on the website and it would only give me the option of a $0- change so I called the 1K desk and asked if I could cancel and rebook, using the credit for the canceled ticket to buy the new ticket. They said that should work fine. Well, in practice, it could not be done. I called back and they had to open a different window to even see the cheaper fares and couldn't get any functionality to rebook into Z with the credit from the cancelled flight. They had to call the "rate desk" to get an adjustment to pull this off even though there was Z5 available.

Is this normal? Is there a better procedure that I should've followed?

Thanks!