Sorry to hear of the experience. 

I've had a reasonable track record using overseas mobile numbers with certain NZ services (eg. Banking).
You may need to call the bank to register the foreign mobile number though as some apps won't allow you to use non NZ addresses. 

My approach has been to lift as many services across to my AU mobile numbers. I keep a prepaid ($10 a year top up) for the last stubborn services and wifi calling to avoid roaming charges. Both One NZ and 2 Degrees will allow for overseas Wifi calling (Spark does not). 

I hope that the NZ operators evolve their policies. I managed to get my 2 Degrees esim reissued when I was in the country a few weeks ago, took 4 hours though. 
One NZ is nicer though - the QR codes are reusable. 

Optus and Vodafone (in Aus) will happily do overseas eSIM activation provided that you meet the minimum points of ID (plus do the facial ID).