You could try to repot it. Make sure that the roots aren't too wet, check for pests, rot and fungus. Plenty of drainage and only water at the edge of the pot or from underneath, never directly on the cactus.
@philstalder Yeah I used to see them forsale here too when I was a teenager, but haven't for years, apparently the story goes hylocereus (the root stock commercially used) doesn't survive well in NZ so most of them rotted and died and became unpopular because of that so the nurserys stopped importing them.
Oh wow. They sell them everywhere here in Los Angeles, but not like beautiful ones you have. I didn’t know you were in NZ. One of my absolutely favorite places on earth. Been there a few times. Good luck on your little marvels. 😃