The insurance company is likely not in the wrong here. I think part of the problem is that, as Brits, we are used to not worrying about this kind of thing. If we get hurt in the UK we get unlimited "free" healthcare (paid through taxes) and there are reciprocal agreements throughout Europe whereby healthcare is either free or has a nominal charge to reduce Moral Hazard. We don't have to think about communicating with an insurance company.

Since moving abroad I have gotten used to carrying my insurance card and calling their number before any elective insurable event takes place. I feel that the OP was unfortunate in finding this out the hard way.