Condolences; sounds like you have your work cut out for you.
Talk to your insurance company for sure, but try to get advice from some independent body too if possible? If there is any sort of an ombudsman that can help you with this? You might have to look around for what's available in your area.
I assume you're talking about some other insurer than Medicare, and I imagine the level of rigamarole can vary widely. If they give you bad news, I wouldn't automatically take their word for it without double checking.
(If you *are* talking about Medicare, be sure to use their help-desk services; they're pretty decent. Also there are volunteer organizations, they vary by state but sometimes it's called SHINE, that can be very helpful in figuring out Medicare.)
As Rose said, the hospital or clinic business office can be very helpful. I had a good experience with that (mine did not help me find funding -- never occurred to me to ask, so who knows what they might have had -- but did arrange a very manageable payment plan once I was sure of the amount I would have to pay, and they were super nice about it).
Be sure to read your insurance contract, however much of a pita that is to do (don't take the company's word about what's in the contract). And read any communication they send you very carefully (I HATE when people send vaguely threatening messages that, if you look at them closely, don't have much of a concrete threat in them, and they just want to scare you while keeping themselves legally CYA'd).
A local senior center might have, or be able to direct you to, some good advice. If it comes down to a legal question, there might be free/cheap help in your area, the state bar association often has a program for very cheap preliminary advice, and re very general issues you might be able to find advice on websites like the one for Nolo Press (use carefully, though!).
It looks like even in the best-case scenario you've got a royal-pita job in front of you, sorting all this out. Pace yourself but stay on top of it and don't let it fester; medical bills can be a nightmare. One day at a time; you'll get through it.
And as Rose said, keep a record of everything!
Good luck.