Hi there. I’m a lawyer at MinterEllisonRuddWatts. Not my area, but I had a chat with one of our IP partners Chris Young. There is some thought and strategy needed as to how best to respond to this sort of letter (they are not uncommon). Chris is happy to have a chat with you (without charge) if you want to give him a shout. His details are on his link here – https://minterellison.co.nz/people/chris-young

Good luck!