Me: 'No, I'm not giving out my details to someone who rang out of the blue and says they are a bank'
Her: 'Can I give you a number to call me back?'
Me: 'No, that doesn't work: how do I know where a number you gave me will go? Can I ring the number on my card statement?'
Her: 'No, because that's a different department'.
Me: 'Well, you'll have to send me a letter then'.
*** Phonecall ends in confusion ***
Not that that solves the problem, because presumably the letter will have a phone number on it, which will not be the main one for the bank, and could be faked, but if a letter arrives, I suppose I will have to extend the hand of trust and phone it...