Pressler & Pressler/ Palisades Collection LLC Won't Leave Me Alone!

Pressler & Pressler/ Pallisades Collection LLC has been coming after me for various debts that I supposedly owe since 2004. At first, being naive, I paid off one debt in full and am $800 away from paying off a (2nd) $6000 debt. In March 2009, my joint bank account was levied in the amount of $1200 for a (3rd) debt that I allegedly owe from the birth of my son in the year 2000. I was on Medicaid at the time but Medicaid no longer has records from the year 2000 so I can not prove it. Being that I can't prove that I was on Medicaid I entered into a payment arrangement with P&P in the amount of $100 per month that was supposed to start on 4/25/09. Today, 4/22/09, I logged into my bank account only to find that it was once again levied by P&P. I called and they can't figure out why it was levied because we have a payment agreement in place. They are going to try to "figure out" what happened. Now, when I got home from work today, I received a notice that I'm being sued by them AGAIN for another (4th) debt that I allegedly owe to Verizon from the year 2002. I really don't know what to do anymore. How can these people keep coming after me again and again for any little thing they can dig up from the past? I honestly can't take this anymore and am on the verge of a breakdown! How can I stop them? Please help!