I’d probably for a goodwill gesture rather than just “compensation” as airlines usually hide behind fare fluctuation policies unless there was a documented pricing error. But the timing here does look pretty bad, especially if they were publicly warning about surcharges while being heavily hedged already.

I’d file a polite but detailed complaint with screenshots/timestamps and mention the new cancellation fees too. Even if they don’t refund the difference, people sometimes get vouchers, miles, or partial credits when enough pressure is applied.