When was the last time you logged into your Yahoo account? If you haven't accessed your account for 12 months, it was automatically deleted due to inactivity and recovery will not be possible.
If you've accessed your account recently, try this:
Send a message to your Yahoo email address and if you obtain an error message informing you that your account is disabled, contact Yahoo using this link. On the contact page, select Account and type your Yahoo email address. Choose Contact a Yahoo specialist > Abuse and spam > Got a message my account is deactivated > Email a Yahoo specialist.