That’s the crazy thing about the US system. For a lot of people things work smoothly like it did for you. Then you have a significant number of other people who get totally screwed with out of network stuff, billing errors and the insurance declining payment for random things. These people now have to have to negotiate often for years, fight collection agencies and often end up owing thousands and tens of thousands of dollars. It’s a big gamble and there is pretty much nothing you can do to protect yourself.