Delete mailbox not working

[darrenings]

Trying to do some admin on my accounts and wanted to remove an old mailbox amber@korde.co.uk.

So clicked on "delete mail box" in the "mailboxes" section which gave me the message:

"The following actions will take effect immediately and can not be undone. Deleting or clearing a mail box account will cause all messages in the mail box to be deleted immediately. Deleting a mail box will also remove any mail forwarders or mail mirrors that reference it. Are you sure you want to proceed?"

I clicked on "Confirm Action" but I am returned to the mailbox screen which shows the amber@korde.co.uk mailbox is still there.

Can you help?