Sorted my problem now. The problem seems to have been because I had used the same email address for both my old fan number and the new one. When I logged in using the email address it took me to the old one.

So I logged in and edited my details to change the email address for the old account to a different email. Then I logged out and logged back on using the usual email address. This time because there is now just one account linked to it, it took me to the right account.

Not sure why this started being an issue in recent months. I've been using the new account for around 9 years and only now has it decided to link my email to the old account.

Don't know if any of that makes sense or applies to anyone else - Bob Banker Spanker - does this situation sound familiar