Same problem, for the last week or so.
Not a new account, we have been sailing MSC for over five years.
I get same “wrong country” error whether using my laptop, iPad or iPhone, and regardless of browser. I have also tried logging in just using cell service and not my home wi-fi. My husband reports the same problem.
I’ve confirmed we are not logged into the MSC app.
We did recently return from an MSC cruise, and the problem started about them. (But I also experienced the same issue a few months ago, no travel in that time frame).
I can log in with a future booking number, but that does not give me access to my full account which is what I want!