It is possible the Original Poster purchased a business class ticket AKL-SYD-PER at the 'usual price' but with the SYD-PER sector in economy.
I just made a dummy booking and it was quite easy to find this circumstance, and it isn't all that obvious that the second sector is in economy - especially since the price is unchanged from options on the same day where both sectors are in biz.
For the OP, what is the letter code on your e-ticket for the SYD-PER sector? That will tell us a lot about what has happened.
I produced this composite screenshot to show the dummy booking I made earlier - the red boxes are added by me and highlight the economy cabin on SYD-PER on this 'business class' ticket:
Last edited by Thai-Kiwi; Nov 19, 2018 at 7:37 pm
Reason: amend pic