PDS Mediation called and said we owe an outstanding fee on a magazine subscription from 9 years ago. The first time they tried to scam $ from us was 2 years ago and we filed a BBB claim and they dropped everything. Now they are trying again and threatening a lawsuit. I think they wait for years until they think people will forget, get scared and just pay them whatever. Last time they couldn't even send us an actual invoice. Scammers!

That is because you have filed a complaint with a toothless organization that has no law enforcement powers.  Here is where you need to file complaints, and if they fail to do the following then they are criminals who are breaking the law.
Federal law (FDCPA) requires them to send you a letter (US MAIL ONLY) within 5 days of their first contact that contains their name, physical address, the creditor’s name, and the amount of the alleged debt.  It also must contains “mini-Miranda” telling you that it is an attempt to collect a debt and that all information will be used for those purposes.  The one other important thing that this letter must also have in it is that you have a right to dispute the debt within 30 days of receipt of the letter and if you do so, all collection activity must be stopped until the debt is verified.
Read up on your rights here, get template letters to send and also make a complaint at this government site:  http://www.consumerfinance.gov/
Also file a complaint with your State Attorney General's office.
List of State AG’s offices:  http://consumerfraudreporting.org/stateattorneygenerallist.php

I got the same call today. A lady called and said she was trying to collect from a subscription from 9yrs ago that I stopped paying on. She said she was a lawyer.  I don't even get magazines! I got a call like this a few years ago trying to get money out of me but I think that number was from WA. I told her she isn't getting a dime and I have nothing better to do but go to court.  I'll see if I get anything else from them.

That I was a part of a civil lawsuit and needed to call them.

Short answer -- IF you were involved in a law suit, you would have a WRITTEN document, not a phone call.