Finally, got the wife's ticket sorted. Tried other cards (visa & mc) several times and got nowhere.

She rang BAEC and explained that the website would not let her change her ticket. She informed them that we had tried ten times over the last twenty-four hours and it just will not work. After being placed on hold for a couple minutes, the agent returned to confirm that the system says that we'd tried ten times and offered to do it for her and waived the telephone fee!