Well, that stinks! However, if the hospital "accepts assignment," it means they are supposed to accept whatever Medicaid or Medicare pays as full payment. If they changed Medicaid companies on you, you should get not only a new insurance card, but also a printed explanation of benefits...things they cover.
Don't worry about the bill. If you should end up having to be responsible for that balance, send them only what you can each month...even if it's only $1 a month...and there's nothing they can do. They can't turn it over to a collection agency or dun you for it, as you are showing "intent to pay."