Natwest seems to have taken to sending me text messages listing three recent transactions (where one is suspicious to them), and asking did you make these? Rep

Natwest seems to have taken to sending me text messages listing three recent transactions (where one is suspicious to them), and asking did you make these? Reply y or n. I can't verify that the text is from Natwest, but it seems relatively safe, as I'm not providing any personal information in return, so this seems a reasonable first line security mechanism. Of course someone could clone my SIM, in which case there's no protection, but it does raise the bar for using a stolen cards, and I think that's the intent. If my bank ever does call me, they have to leave voicemail because I don't answer calls from unknown numbers. And then I call back using the number on the back of the card.