Rephen Law Firm Called Claiming I owed $170.01 for a $20.01 returned check...Never received any documentation, threatened... New York, New York

This has been quite some time ago, so the details are a little sketchy, but I was just wondering about something lately and decided to look it up.
A lady from Rephen Law Firm called me and claimed that I owed $170.01 for a returned check for $20.01. At the time of the call, I didn't know much about the ways of the world, so when she threatened to take me to court, I buckled. She told me that I could pay the debt and settle out of court, but I couldn't mail her the money. She insisted that I pay with credit card. This was very odd, since most collection agencies want some kind of guaranteed funds (cash, money order).  I just kept thinking about how this one little check could ruin my credit history.
Honestly, I didn't even know that I had a returned check.
I thought all of these details sounded just a little fishy, so I called the company that the check had been returned on. I'm thinking it was telecheck, but I can't be sure. Anyway, they company told me that they do use that company, so I started to think this was a real law firm. I took an advance on my paycheck to pay the $170.01 because the lady on the phone gave me three days to pay it.
I have not received any information by mail to this day. Perhaps I should look them up and give them a call. I know I still have that telephone number written down somewhere.
I'm a little braver now, and I think I could straighten this, "law firm," out with my lawyer.