When dealing with companies like banks, insurance companies, telecom firms etc. I accept that sometimes, it is irritating, but necessary, to waffle through some security checks.
Today's caller (they're calling me) demanded the following...
Full name
User name
4th & 7th from password
Home telephone number
Post code
How do I pay my bill
Last 3 digits of sort code
Last 3 digits of bank account
I failed on the last two, no cheque book on me, so they couldn't discuss on the 'phone so, instead, sent me an email.
"Just to let you know, we made an error on your last bill". I'm getting a refund plus a credit as a good will gesture.