Yahoo_Technical_support_1-888-521-0120

Your account can also be blocked if yahoo suspects that your account is being compromised. In such situations to safeguard your interest yahoo will block your account and you will need to provide a verification code to access your yahoo mail account. If this is the case change your password and immediately call yahoo customer support for further help and assistance.

http://www.emailphonenumber.org/yahoo-helpline-number.html