The fact that I STILL get this from Air NZ when trying to check my flight credits
"We are holding your booking in credit and are working on functionality to enable you to rebook online. If you urgently need to use your credit please call us."
instead of it actually telling me how much money I have in credit for the booking in question.
Not to discount your frustration, but it is a complex situation, particular if it was international bookings due to how taxes and levies are applied.
All they needed to do is refund the money. They already manage that when they need to (including taxes etc)...so they must have the functionality somewhere.