My iCloud IMAP email address is not mine and I cannot edit it

In 'Manage my Apple ID' I saw that one of the 'Reachable at' email addresses is for someone I have never heard of, using an iCloud address (I don't use iCloud).

I logged into iCloud for the first time (Windows laptop using Chrome) and the iCloud IMAP email address is for this same person. I'm not referring to the aliases, it's the actual email address registered against my name, but it's not me - see screenshot below.

I have spent AGES reading community posts and going through iCloud and my Apple ID to work out how to change it but I cannot see any option.

Thanks