Nationwide Eventually Did Listen
YESTERDAY I finally managed to get some important feedback through, after failing to do so over the phone and even in person. I cannot pronounce or recall the name of the lady who helped me do this (she's Indian in origin, bless her!) but she took note of what my wife discovered and I reported. It was a security problem.
Today, as she promised me, I received a message from the "IT team":
Miles better than their original nonresponse! The message they sent also corrected the rogue behaviour that we reported, so we probably had an impact on millions if not billions of messages to be sent to millions of people in the future.
Every little feedback can have profound impact, even if companies don't like to acknowledge this. █