Not OP, but I think they mean changing their mobile number setting inside of their online accounts is impossible. When they moved, they got a new number format but their existing account won’t let them change the format.

Yes.. It is near impossible to change a phone number for most accounts. My US banks would not allow for the same amount of digits as my European phone number had. Wiring money from my own accounts wanted to send a 4 digit pin to my US number which would not work in France. You seem to imply that in 2023, we are not capable of making a banking application accept more than one format of phone number. And the fact that google cannot figure out I live in another country (and I have to enter a bank card with address in an app store or else I am blocked from certain apps) is laughable.

I mean, why would a bank care about phone numbers outside of the country it serves? Do you expect a US bank to recognize the number systems of every single one of the 195 countries out there when 99.9% of their customers live in one? Do you expect a French one? An Ethiopian one? It's not like they lose a whole lot of business if they don't support it; it's an edge case at best, especially when most people do get new phone numbers when they move.

And Google certainly knows you live in a new country, but you likely have to accept new Terms based on the country you move to, and there are more than likely fraud policies in place specifically to prevent people abusing a system like that to get lower pricing. The required step is there as policy, not a technical necessity.

Google certainly moves accounts between countries automatically: https://news.ycombinator.com/item?id=27560705

At least according to that they won't ask you to accept new ToS, probably due to the fact ToS allows them to change ToS at will.