So the update is (as expected) the phone call was the usual painful fun with lots of long periods of being on hold for no apparent reason. That is of course when a human actually finally picked up the phone. Lots of "All agents are busy. Please call back later. <hang up>".

Anyway, the short version is they decided (and I agreed) I was better off buying a new ticket and just cancelling the existing one. So that's what I'm going to do now.

f4free- your explanation of their inability / refusal to make any changes that result in a lower fare was spot-on. And chris63 as you say, I will take a screenshot once I make the new booking and then ask them to cancel the first one.

All this drama just to change one ticket by one day. Thank God the Chardonnay at least arrived as was promised!