Cannot reset security questions

Contact Apple Support: Contact Apple for help with Apple ID account security

However, Apple Support may not help you, as according to Security and your Apple ID:

Without proof of your identity via security questions and other carefully selected criteria, Apple Support can't help you reset a password or perform any other actions on your account. These policies are audited and reviewed on a regular basis.

I can understand that.

If you are unable to reset the questions online though, you need to contact Apple Support to see if they will reset them.