All insurance companies play this game at one time or another. They figure if they can get you to pay the bill, why should they? Payment for charges takes up to 8 weeks or longer, but a denial comes immediately if not sooner!
As long as you notified the insurance about the hospitalization the next business day ( or at least called your PCP if they're not the attending doc in the hospital) to get "authorization" , the insurance doesn't have a leg to stand on. If you didn't call your PCP, call them tomorrow and ask them to call the insurance and give them "prior authorization" - which really isn't prior, but as long as they call, most of the time the insurance backs down.
The other alternative is to call member services at your plan and explain WHY your wife is in the hospital and ask them to reconsider the charges. Sometimes, the idiot who gets the claim (here in NY, they hire college kids to process claims, which BUGS me but that's a whole other story!) looks at the provider wrong - some providers fall under more than one heading, and it effects the way the claim is processed. If they refuse to reconsider the charges, ask them for the appeals process and appeal it formally.
Whatever you decide to do, make sure you notfiy the billing department at the hospital so they don't harass you about paying it. Tell them you're fighting with your insurance and will keep them informed. (Otherwise, you could end up in collection, which is a headache!)
I know this is all a pain the *ss, especially now, but DO NOT back down! Insurance companies count on p*ssing you off so you give up and pay the bill. As long as you do what you're supposed to and stand your ground, they'll lose! If the person you get initally isn't helpful, ask for their supervisior. If that doesn't work, wait ten minutes and call back.
Good luck! I hope your wife feels better.