Would you pay the $218.30 or fight it? And, please tell me how to fight it from this point on!

[faeryedark]

No. I would not pay it. For one, I'd be worried that they'd say they nver got it. I would threaten to report them to the appropriate agency for violations in "harrasing" you for a bill that's alrerady been paid and you've sent proof of over and over again.
There are lots of laws out there to protect you.
I'd also file a dispute with whatever credit bureau you need to ASAP. let them know you're done playing.

[billig]

My advice is a mix of everyones advice:
DON'T PAY IT!
If anything, spend $200 on an attorney telling these idiots where they can shove it.
First off, I just learned that getting the return recepit isn't the way to go...of course now I can't remember what it's called, but you can pay for another way that the postal employee notes when the letter was delivered. Then it doesn't get turned away.
I'd do all of the above suggestions...contact the atty general for your state...get a free 20 minute consultation with an atty...when all is said and done, then go for the tv crews cuz there's nothing like bad press to motivate someone!
And if the credit dingdongs call you again, just say you're contacting your attorney to sue so you can't talk to them anymore. There's probably some law about something about that, but you're only saying "I'm GOING to contact an attorney"...nothing definitive there.
And while you're talking to them, start harrassing them:
"What's your name?"
And what's your employee number?
You can't tell me?
Then how am I suppose to refer to this call in the future, am I suppose to say "a girl named Jenny called me"?
stuff like that...all pertaining to your case, but just wasting their time for the fun of it.

[neglectarino]

Thanks for all the advice. I've shown this thread to DH, and we are definitely going to contact the OB again and again and again... We're going to resend all documentation to both the OB office's billing manager (thanks, Google!) and the collection agency. It's still not showing on either of our credit reports, which I find very weird.

Here's a letter that will send the CA back to the OB's office. You can add that you have previously sent proof of payment to both the CA & the OB's office, but I wouldn't resend the proof with this letter. Make them work for it now. Mail it certified return receipt, include any reference number for their collections, & don't sign the letter--use some fancy font if you like. You never know what they can do with a signature if they are so inclined (legal or not).

To Whom It May Concern:

I dispute your claims in their entirety and request validation pursuant to the FDCPA.

All future communication with me by you is to be in writing only. I will not accept or respond to phone or email communication.