Freak out your customers. Ask them everything twice.
When I call my bank they ask me to enter my debit card number when as I am connected with associate he asks me the card number again as well as last numbers of SSN for verification purposes. Same happens in other cases – for example just today online Skype support would ask me to enter Skype name and email and when they ask me exactly the same stuff again. I find it very annoying and somewhat disrespectful.
If you want to show your customers respect and what you value their time do not ask them information what you already have on file or which they already previously provided. If you need to validate something for a change you can ask some related question, for example “do you still live at Rose Rock Cir”. This is understandable and not nearly as annoying. If you need to check something for security purposes why not to tell that, people like to see you care about their security or at least understand it. Yet if you validate something for security purposes you do not have to ask the whole thing. For example being asked my address for verification purposes I often would tell my house and street number yet the phone agents would often also want city and zip. It is a waste as there are only couple of locations in US for my street address (excluding city) so adding city does not increase security, and Zip is completely redundant.