I have been trying for several weeks to get someone else's name off of my email. Where do I find setting?

My email account was compromised several weeks ago while I was out of the country. After some difficulty I was finally able to reset my password. First, problem, since then another unknown person's emaill address pops up in the address line when someone replies to my email. The other person's email address is also appearing in my yahoo account information as a "default" email address. Second problem, all contents of my Contacts were lost as well as mail in the inbox and sent folder prior to the date I reset the password. How can I get rid of the unknown person's name appearing in my account and is there a way to recover my lost contact list and inbox and sent emails? Is there a way to contact Yahoo? The other persons name may be a systemic problem.