Thank you for posting. I'm sorry if you're unable to view your bills online.
If you send me your details, I'll be able to give you a hand getting that fixed.
I have sent you a private message with instructions on how to contact the team. You can access your messages via the envelope icon at the top right of the screen, or click on this link, Private messages
Thanks for taking the time to reply to all of my private messages allowing me the time to fix this for you.
In your original post you asked how can this particular error message be fixed so I'm replying up here so the next person can see how, if needed.
We can remove the old accounts at our end but if that still doesn't allow you to view your main account, we would look at deleting your MyBT account and getting you to set it up again. This can be the quickest way of resolving it.
Take care and have a great day.