Hey, It's difficult to recover this but you can try at once. Follow below mention steps:
*Go to the Sign-in Helper.
*Enter your phone number or email address.
*Click Continue.
*If prompted, enter the CAPTCHA code.
*If you can receive text messages to the number listed, click Yes, text me an Account Key.
*After this, you can recover it.
Still if you are facing any kind of issue visit here http://www.yahoosupportnumber.net/yahoo-toll-free-number.html