If you encountering Yahoo Sign In issue then do check the entered details which you have provided in the Yahoo Sign Page as some time when we enter wrong details then we usually face the sign-in issue. If you have entered the right details and then to you are unable to sign in the account then just make a call at Yahoo Phone Number i.e. +1-855-479-3999. https://www.mailsupportn...omer-service-number.html