Welcome to the community and thanks for your post!
Sorry that you're going round in circles trying to add BT Sport to your existing services. On which platform would you like to watch BT Sport? (BT TV or Sky digital platform)?
Check this link out and let me know how you get on: How to watch BT Sport
Cheers, I have tried that, but it gets to a page to offer a whole new connection, not to alter the one I have. Thanks.
Are you signed in to MyBT when clicking the links?