I'm trying to use this for a flight this afternoon and despite the first page of the process confirming "you can change to another eligible flight on the same day for free", when I click through it says there's a £100 change fee (that's apparently normal and usually disappears later) but when I go through to the final page it comes up wanting a £560 payment with an apparent fare difference of £487 and an inexplicable £73 in "additional fees, charges and surcharges". Do I pay and request a chargeback? Call and hope someone competent answers?

On that final payment page it also tells me my fare rules for the original flight which includes "Free changes on the day of departure provided changes are for same date/cabin/route/airport"

What a joke.