Happened to me the other day. I went to https://expresslane.apple.com/Issues.action and asked what to do there. Less that 24 hours later I got a response to go to the account management on the page linked above, select lost or forgotten password, and then you will have the option to have an apple rep call you back. Most times there is an option to have them call you immediately. From there they will reset your questions if you can prove a few thing to them. Give it a try, it is fast!
Oh... answers are case sensitive. Rep I spoke to suggested to use one word answers to the questions and use all upper or lower case. When you answer the questions again it is probably best to just write them down EXACTLY as written put it in a safe place.
Because I can not remember my answers to the security questions that was asked on Itunes and I haven't been able to purchase any tunes with my $136.00 in credit for weeks, there is a way to resolved the problem, that is for me. I turned on Itunes and went into "Account" and added a credit card and then I updated. I then tried purchasing and it worked! It will bypass the security questions. Then I went back into my "Account" and deleted the credit card and the security question box never appeared again. Hope this helps others, it did for me. Good luck!
Usually you will need to contact iTunes store support but this workaround may help:
-On the device/computer that is asking you for the security questions go to "settings", > "store" > tap the Apple ID and choose view"Apple ID" and sign in.
- Tap on payment information and add a credit/debit card of your preference then select "done", in the upper right corner
- Sign out and back into iTunes on the device by going to "settings"> "store" > tap the Apple ID and choose "sign-out" > Tap "sign -in" > "use existing Apple ID" and you should be asked to verify your security code for the credit/debit card and NOT the security questions.
- At this time you can remove the card by going back in to edit the payment info and selecting "none" as the card type then saving the changes by selecting "done". You should now be able to use your iTunes store credit without answering the security questions.