he can't delete your secret question. he just change it. but if you click the it's not my secret question, your original secret question will take place again. go to this link and click forgot password then choose i can't access any of above... when you're on the secret question page click this is not my secret question hope it can help...
I am afraid that you can't do anything. If the hacker did all what you said, not even the yahoo support can help you.
I had the same problem with my yahoo account. It was only hacked once but I just shut it down and started over. Its a lot less stressful.
Hacker can change everything, but he cannot change the history. And now a days all mail service provider looks for history of operation when it is under taken over by anybody.
My sisters account also got hijacked what is even worse is that after they took it they start spaming her friends as if she was in need of money and asking for her friends support to send her money to some bank account. She signed up another account and notified the situation to her friends. It happened after she clicked a fishy link and updated her info there.
That hacker must be really talented. Try opening another email maybe you should open up a Gmail account and see how it goes..
Check this great tutorial, it may help you for sure : How to get back your Stolen/Hacked Email address Best,,
My guess is that you have spyware on your computer. You may want to take care of that because any other accounts you open may get hacked too.