If you haven't logged into your Yahoo account for 12 months, it was automatically deleted from the server.
Unfortunately, you will not be to recover your data.
You must contact Yahoo to to know more about the reason. It is possible that your account was deactivated due to a violation of their Terms.
To contact Yahoo, go to this link. Select Account and enter your Yahoo email address.
Then choose Contact a Yahoo specialist > Abuse and spam > Got a message my account is deactivated > Email a Yahoo specialist.