I think you are missing the point of the Nationwide cash card account, it meant for people on low incomes who don't qualify for their main (flex) bank account. Therefore the changes are to the advantage of the people that the card is aimed at. When Nationwide stopped free worldwide foreign withdrawals on their main (flex) account last year I though it wouldn't be long before they stopped it on their basic (cash card) account.
You've been lucky to be able to use it over the years as the equivalent of pre-paid currency card with no fees, but I suspect your free ride is now over no matter how much you try to protest.
