I once had to call my bank a few years ago to disable my debit card. The reason was that I inserted it in an ATM and the ATM had chosen that exact moment to malfunction and shut down!

The operator on the line asked me a ton of questions starting from my user-id (but not password), date of birth, full name, father's name, place of birth, type of account and many others that I don't remember now. Only after I correctly answered all these questions, did he start acting on my instructions.