On yahoo, I have an account that I know the password to but can't sign in. I've changed my number so this solution is a bust; also it asks security questions but I don't really remember the answers. Is recovery impossible?
Unfortunately, if, when you created your account, you have not registered an alternate recovery email address to which you have access to receive an account key, you can’t prove that you are the account's legitimate owner. Hence account recovery is absolutely impossible and there is no way around it.