Read the link?
"Refer the vehicle to a VIN issuing agent (VTNZ, VINZ, NZAA). They will inspect the vehicle and seek approval from NZTA to issue or re-issue a VIN plate."
Basically as above, take it all to a repair certifier, both vehicle identities, all the paperwork to prove you own both and go from there. Good luck.
As for R100's phone calls, the repair certifier probably figured you were being a dick.