Security. They've heard of it
Phone call from my soon-to-be former mobile phone provider. (I'd called the previous night to get a PAC and cancel the contract and they were calling with an "improved" offer to persuade me to stay. I won't be doing so.)
Them: Hello this is [name] calling from [network]
Them: For security reasons can you confirm your date of birth please?
Them: Please tell me your date of birth
Me: Err no, you tell me what you think it is and I'll tell you if you're right. I have no way of verifying that you are from [network]. How do I know you're not phishing for my personal information?
Them: Ok, I understand that. Could you tell me your postcode instead?
Me: I will happily confirm that what you have on file is correct but I'm not giving you any personal information
Them: I can't continue the call without confirming the details
Me: You're the one who has interrupted me for a conversation I don't particularly want to have. Your problem.
I really can't understand why they can't grasp the idea that if they initiate the call, it's them that need to prove their identity to me. I tried to feedback to them via Twitter and they missed the point there too. Muppets.