Please help with INSANE surprise bill (Follow Up)

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A few years ago, my mom was in a car accident and was taken to a hospital in an air ambulance. We received bills, and I always sent them to insurance. My mom doesn’t speak English so I was having to deal with exchanging information. We hadn’t heard anything in years and assumed all was taken care of. However, we just received a bill in the mail stating that the air ambulance company sent the debt to a collection agency. The bill is for ~$33k, but they’re offering ~$19k if we pay lump sum. We have since changed insurance. We live in Tennessee, but I’ll have to check where the accident happened. If needed, I can edit this post with other pertinent information later.

My questions are:

What should be the first course of action? Do we send this to our new insurance, and let them determine if this is a legitimate obligation to pay a debt?

If the debt is legitimate, should we let insurance do all the talking, or since this happened before our coverage with them, will they take no part in discussions?

Would it be foolish to contact this collection agency without a lawyer?

Could we negotiate low monthly payments, or would declaring bankruptcy before anything else can happen be the best course?

Addition

New pertinent details:

We called the insurance company where the policy was active at the time, and they could not find any claim records from 2017 so they told us to contact the provider because it is their responsibility to file a claim. The date of service was from July 2017.

We called the provider and they were able to pull up payment records where health insurance paid them $5,000 and our auto insurance (at the time) paid them $10,000. These payments happened around October 2017. They said there was an adjusted amount for $2,000 (is this balance billing)? They would not give any details for the remaining balance and said that we would have to call the collections company for balance information.

I am not sure how $2,000 turned into $33k and frankly, I am overwhelmed and afraid to call the collections company.