Hi
Flew to Chch in May. Emailed customer services and they upped our allowance to 30kg each + the 7kgs hand luggage. Just about to leave home, weighed the bags and they came out at about 150kgs (for 3 of us)
. Took it all anyway and at checkin the lady looked at us, said OK that weighs 90 kilos and let us through! She also put priority stickers on the bags so they came off the plane before we did.
I think we were especially lucky but I would try emailing their customer services and see what they say.
Good luck