I think the answer you are not wanting to hear is that you owe the money. But more than likely you owe the money.
But if I were you, my first step would be to call the hospital and discuss the matter. Now maybe you can work out a payment plan or something. No way for me to know that. Maybe they'll just demand it all up front.
However, so far, it's been a year, and this is supposedly the first you heard of this bill? I know I get EOB's from my medical provider. I am well aware of what they pay and what they don't. What's it say on that paperwork?
You never received a bill for 12 months straight? That seems really very odd to me.
You easiest option is to pay the bill and put it into your rear view mirror. Other others, are to see about a payment plan, declare bankrupty, or I suppose you could just not pay, not show to court, and move to another country. And I'm kidding, and not actually suggesting that. But I mean what options or rights do you think you have when you owe someone money?