Resetting my security questions

My problem is that i have logged on to the app store and tried downloading pro tube app at 69p. Then for some strange reason it says i need to answer 2 security questions i am pretty sure i have not entered before, and so now i cannot purchase this app because i cannot answer these questions.

I have logged on to appleid and tried to look how to reset the security questions but to no avail. This is stupid as i have already logged on using my password. Any clue would be appreciated. Thanks in anticipation.