freitasm:
Off topic - perhaps create your own thread but I have contacted Kogan PR after your post and here's their reply:
Yes - Kogan Mobile does support VoLTE in New Zealand!
Vodafone’s 4G Calling (VoLTE) deployment is now live across New Zealand, which is available for Kogan Mobile customers as well.
Note: Currently, iPhone users will need to switch VoLTE on manually. To do this, customers can simply look under Settings > Mobile > Mobile Data Options > Enable 4G Voice and Data.
For Samsung handset users, VoLTE is set to be default on for VoLTE capable devices, so customers with an S9 or S10 will see “VoLTE” on the top of their screen.
Thanks for that; had not seen your reply until today.
Given it's still not working I'll start another thread to see if anyone has any specific ideas. (I had assumed I was on-topic, because I understand Kogan uses Vodafone's network, including its provisioning of VoLTE.)