How to reset the security questions?

Dear Sir/Madam,

I have 7 Apple IDs and when I logged into these accounts in the Apple website, Apple required me to choose the security questions (all three questions?) and type the answers.

At that moment, I didn't care about these questions and just typed something as the answers that I didn't remember.

I sold my iPhone 5S and still kept my iPad 2.

I phoned to Apple support today and the support (from Singapore) gave me useless responses.

One staff asked me to log into my account, told him the PIN and switched on the iMessage (fail to log on due to FaceTime server error) in the iPad 2 to have a question reset but hanged up the call suddenly (very impolite).

Another staff asked me to log into my account, told her the PIN, told me the method "iMessage" didn't work as it was available for iPhone only and told me to log into my account by my own using the iPad 2 for more than 15 days (so that Apple will have my record) in order to have a question reset.

Can anyone tell me how to reset these security questions in order to change the passwords for these accounts?

Thank you very much!

Best Regards,

Chris.