1. It's not up to NZ phone agents to provide copies of the law to you.
2. A 30-second internet search produces a copy of the US DOT Warning Letter of 3 April detailing the rules (which have been in effect since 2011) and making it very clear that they apply to tickets originating in or destined to the US https://www.transportation.gov/sites...3%202020_0.pdf/

So, what to do:

1. Initiate a chargeback with your credit card issuer (bank). Be prepared to provide a copy of your e-ticket receipt, the flight cancellation notice, and a 1-sentence summary of your request and denial (better to do this in writing, but too late now).
2. File a complaint with US DOT (online form).