Sorry, I had "Tennessee" written out and I don't know what happened.
The statute of limitations for a lawsuit is 6 years in TN. If the default was less than 6 years ago then that defense isn't helpful. Hence the question about the state.

Yes, I've been served a summons. It's in General Sessions Court, which is kind of like Tennessee's version of small claims court. The maximum amount is $25,000. This suit is for $817. It instructed me to appear and answer, but someone who worked in the courthouse recommended filing a written answer, so I did.
Here's a guide to TN small claims:

http://www.tncourts.gov/sites/defaul...-_may_2013.pdf

The statutes that cover small claims are:

Tennessee Code Annotated, Title 16, Ch. 15, Part 5, Sections 501-505; Title 16, Ch. 15, Part 7, Sections 712-735; Title 16, Ch. 15, Part 8, sections 801-807; Title 16, Ch. 15, Part 9, Sections 901-905.

Which you can find at:

https://law.justia.com/codes/tenness...16/chapter-15/

You can also get a copy of your local court rules from the court, maybe from the court's website.

As far as the medical records go, I may be able to get them if I keep pushing, but everyone I talked to acts like I have to go through this sketchy law firm that owns the debt.
I'm guessing that "everyone" you talked to does not include going up to the records counter in the hospital and saying "I would like copies of all my records. Please give me the authorization form to sign." Then you stop talking. No need to explain why you want them. It's your right. See TN statute 68-11-304:

https://law.justia.com/codes/tenness...ter-11/part-3/

a hospital shall furnish to a patient ... such part or parts of the patient's hospital records without unreasonable delay upon request in writing by the patient
Your written request is the authorization form that they hand you. You might be charged a fee for the copies.

If your medical records confirm the treatment, you probably would be wise to just pay up and get the lawsuit dismissed. If there are no records, find the billing department and start asking questions.

One important thing to keep in mind: the JDB's primary claim is that they DON'T own the debt. So the usual defense may work here. That's partly why I'm confused.
It's possible that the hospital just charged off the account and didn't actually sell it off.

According to the guide:

Seeing the proof ahead of time saves time in court. The judge does not want to waste time while you look at each other’s proof. Showing proof to each other before court gives you a chance to see what proof the other side will use.
That implies that a certain amount of "discovery" is allowed even in small claims which means that you can send the plaintiff's attorney a request to product documents that might help you understand what's going on.

Rule 34.02 gives you an idea of how it works:

https://www.tncourts.gov/rules/rules...procedure/3402

Here's a sample request that gets served on the Plaintiff. You can modify it to suit your purposes:

http://www.putnampit.com/coomer2/Pla..._documents.pdf

Come back to this thread if you need more discussion.