I failed at adulting. What should I do next in this situation?

So, I screwed up and didn't pay a medical bill basically forever. I ignored statements and phone calls and eventually I got a letter from a law firm saying they'd been authorized to start a lawsuit. I immediately went into the medical system's website and paid all outstanding balances. But it didn't stop there... A few days ago I got a business card from a process server taped to my apartment building door with a number to call them. I checked the county court website and indeed there is a suit filed against me in small claims court with a court date in late May.

What do I do now? As far as I can tell I've paid all my debt. Do I...

1. Call the process server? Do I have to, since I already know when the court date is?
2. Call the law firm? Send something in writing with the receipts from my payments? Are they likely to drop the suit then?
3. Call the original creditor (hospital system)? Or go there in person? (I'm concerned that doing this in writing is not enough time prior to court date.) Do they have the power to call off the suit?

Let's say this goes all the way to small claims court. What happens then? Do I need a lawyer? Do I show the judge that I've paid it off, the judge says yeah ok, case dismissed? Could I be punished further? The amount itself is no big deal ($650) but I don't want to pay it twice.

I know this is a very dumb terrible stupid thing to do, and I am very financially responsible in all other areas of my life, so no lectures please.