I had another almost 2-hour chat with them yesterday, and I have now given up on them.
They tried to say that the resolution was to use IMAP! On further questioning, and with me telling them that this was not a solution, this is what they then said...
"There have recently been restrictions placed on POP access due to platform/mailbox abuse affecting multiple mailboxes from connections world-wide. For security reasons users are recommended to disable POP clients
and switch-to an IMAP account on the client for access to new/recent mail. IMAP has additional benefits such as the access to folders including Spam and Sent as well as the Inbox".
"This is something which is being reported on a wider range hence a concrete fix would be on its way but again given the fact of the impact, this might take some time during which we really don't want you to stop using emails over your preferred method."
