Your situation is not unheard of. This link will take you to an article (that I recalled reading a couple of years ago so just now Googled it)
One of the reasons I'm pointing the above writing is I'm wondering if your situation may have been like this with a subtle sign that you hadn't thought of to look for.
He missed the 18-by-24 inch sign in the lobby. Under the heading "Thank you for choosing us for your health care," the sign says services may be billed as a hospital charge, and hospital emergency room co-payments, co-insurance and deductibles may apply.
Note to anyone reading any posts by me:
I came to these forums seeking advice for myself. I have found many other interesting threads. If I participate in your thread, remember that any responses I give should be considered my opinion only, and are NOT legal advice.