How can I revert to BT Yahoo Mail Classic?

What a crock Yahoo are. I only signed up because there was an assurance that you can revert at any time. I have given it a go and don't like it for a number of reasons. Well bye bye yahoo. I don't like being treated like a child nor do I like being tricked into something. I will revert my computer to a previous point and if that doesn't work hello to MSN!