If you forgot the answers to your Apple ID security questions - https://support.apple.com/kb/HT201485
Frequently asked questions about Apple ID - http://support.apple.com/kb/HE37 --> Can I change the answers to the security questions for my Apple ID? --> Yes. You can change the answers to the security questions provided when you originally signed up for your Apple ID. Go to My Apple ID (http://appleid.apple.com/) and click Manage your account.
Kappy's user tip: Some Solutions for Resetting Forgotten Security Questions - https://discussions.apple.com/docs/DOC-4551
KingPenguin 02/2015 post - https://discussions.apple.com/thread/6829577?answerId=27660375022#27660375022
Rescue email address and how to reset Apple ID security questions - http://support.apple.com/kb/ht5312 - "If you can't recall your Apple ID security questions and answers, the optional rescue email provides a way to reset them. Additionally, all future security-related emails for your Apple ID will be sent to the rescue email address."
Jan 2014 post about contacting Apple to reset security questions - https://discussions.apple.com/thread/5798365?answerId=24543247022#24543247022 and https://discussions.apple.com/thread/5838743?answerId=24671039022#24671039022 and related post, Feb. 2016 - https://discussions.apple.com/thread/7375427?answerId=29465949022#29465949022
If none of the above work, contact iTunes Support at http://www.apple.com/support/itunes/contact/ and follow the instructions to report the issue to the iTunes Store.