It is a bt e mail address and I have had this before. I managed to sort it but can't remember how I did it .
When I asked you if it was a Yahoo email account or a BTYahoo email account you replied
"Thanks do much for your help. It is a yahoo account and even after clearing cache it still redirects me to bt yahoo"
If you had given the correct information I would not have suggested that you try and log on via the Yahoo links that I posted!
In which case https://home.bt.com/login/loginform?TARGET=$SM$https%3A%2F%2Fsignin1.bt.com%2Fbtmail%2Fsecure%2Femai... is the correct url to login with. There is absolutely no reason to use a Yahoo url.