They may be saying the hospital or some provider within it was out of network, challenge this on the grounds it was an emergency. Challenge everything on the grounds that it was an emergency.

We had excellent grounds to challenge a few of the charges from the hospital (clear billing mistakes), but it never got to the point of evidence. We just called to argue and they instantly dropped them. I would strongly advise just calling and complaining and seeing what that gets you.

Many hospitals offer interest/fee free installment plans, you just have to ask.

I am, by nature, a mild mannered (perhaps even meek) person, but let me tell you that just doesn't work with hospitals and insurers. Their process requires you to take an adversarial/demanding role with them otherwise you will not just get billed unnecessarily but also not receive all the care you are entitled to.