If per chance you are trying to reset a sub-account email account you need to use the security answers for the master account.
You can only change the security details for MyBT by logging onto your MyBT and going to "your account" then "your profile". You can not, as far as I am aware, change the security details for your email via that route.
If you are on the BTMail system have you tried this link
If you are on the BTYahoo email system have you tried this link
Obviously the answers to security questions should not be visible as that would defeat the reason for having security questions as anybody who managed to gain access to your account would be free to change them.
If you are on the BTYahoo system see this link
As I said, the only other security question that I am aware of is in your MyBT profile
The only other way of changing any security problems would be by contacting BT and they should be able to help, albeit they may have to send you the details to the account holder's (your) home address