NCL apparently no longer gives port charge refunds. I didn't get a Ponta Delgada refund (Dec2022, as mentioned by Middleager), and I received the following NCL reply for a recent (Apr2023) missed Nicaragua stop:
"Please note that under the terms and conditions of our Guest Ticket Contract, Norwegian Cruise Line in its sole discretion may cancel, postpone or delay any port of call without prior notification.
...
Respectfully, and in light of the above, we are not extending any form of compensation and appreciate your understanding in this regard."