My complete BT Yahoo mail inbox transfered to Windows live mail. How do I get it to go back to BT mail classic?

I don't what I did wrong but suddenly my entire BT Yahoo inbox dissapeared and turned up in Windows live mail which I had never used. Now I have messages coming in on two programmes and I can't file mail away in my BT ,mail folders. . I really want to get back to the way it was Any ideas?