RTW Classic Reward - Just received an email that we’ve been downgraded from P to Y cabin

TL;DR: Originally booked Premium Economy on JAL for our SYD > TYO flight, but just got an email from Qantas saying those seats are no longer available, and we’ve been downgraded to Economy. What are our options?

Hi everyone! Hoping for some advice on a frustrating situation.

Last year, I spent months researching and planning a OneWorld RTW Classic Reward itinerary for our April honeymoon and managed to secure the flights we wanted—mostly in Business, with the exception of our SYD > TYO leg in Premium Economy.

Today, I received an email from Qantas saying that P cabin is no longer available, and we’ve been given the choice to either move to Economy or cancel for a refund. Obviously, cancelling isn’t an option for us, but has anyone successfully negotiated an upgrade instead of a downgrade in a similar situation? It seems odd that they’d just bump us down to Economy when this is an issue on their end.

Also, would this be something to take up with Qantas or JAL? Appreciate any insights!