No matter who hacked your password,  the hacker can't change your secret answers, zip code, and date of birth...unless that person knows you very well. If that e-mail account is that important to you, the i'll suggest you to call Yahoo customer service @ (408) 349-3300

here are few things that might help you.

701 First Avenue
Sunnyvale
California
94089

Numbers:

Phone US: (408) 349-3300
Fax US:408-731-3301

Yahoo! Contact Hours:8:30 a.m. to 5:00 p.m. PST

Yahoo Email:

spoof@yahoo-inc.com - Got an email from someone asking for your account information report it!
messenger-security@yahoo-inc.com - Questions about Security or a vulnerability!
security@yahoo-inc.com - Report a technical vulnerability!

Forms

http://add.yahoo.com/fast/help/us/edit/cgi_feedback - Sign-in and Registration Help Form.
http://add.yahoo.com/fast/help/us/security/cgi_feedback - Security Feedback
http://add.yahoo.com/fast/help/us/mesg/cgi_log - Invalid Login
http://add.yahoo.com/fast/help/abuse/cgi_abuse - Report Abuse