If the system is telling the A3 agent that you were booked into a particular class that isn't creditable then they can't help you.
You can try emailing United and NZ's customer services asking them if they can check what class it is meant to cross consider as, or the transformation table UA - NZ in general, but the likelihood of getting a good answer, or quickly is slim.
Probably start with NZ first as the operating carrier they are ultimately responsible for the mileage earning.