Seems to happen all the time with either my bank or credit card or insurance company ringing me. I haven't asked them to call and, invariabily, they're trying to flog me something.
I've no idea that they are who they say they are - but the immediately damand: my full name, address, date of birth and password on the account.
Just had one now from the Halifax.
"Hello Miss X this is Simon from the Halifax. Before we continue can I just take your full name, address and date of birth?"
Me: "can you tell me the reason for the call please?'
simon: 'no, not until you answer the security questions.'
Piss off!