You raise a good point learner. I had a phone call from my car insurance provider (was thinking of changing to another provider) and like you I started to answer security questions without thinking that this could be just anybody on the phone.
But if its any consolation I was thinking of getting an M&S card and you have decided me against it. So one up to you! 
Soops kitchen, a place of reflection, refuge and at times revelry.







