I used to be a Totalise/Madasafish ISP customer and had several @totalise.co.uk email addresses.
One was directly associated with my account, the other two were 'free'.
I just found some notes relating to these accounts, suggesting that the addresses may still be valid, so I thought I would send a test message to see if they were indeed 'live'. The account-related email was bounced back as undeliverable, as expected, but the other two did not, which suggests they are still viable addresses.
I have tried logging-in to the Plusnet webmail, without success, but my notes do not suggest the password/s used.
It would be wise to check that no-one is still trying to contact me before asking if they can be disabled, but that will require me to log in.