Portfolio Recovery Suing Me

I received a letter and sample lawsuit from the legal department for Portfolio Recovery. It stated that if I did not contact them by a certain date to pay off the balance or to make acceptable payment arrangements that they would file a lawsuit against me. I did in fact contact them because I knew that I did owe for a Sears credit card some years ago. I am now learning that I should have asked for a debt validation letter after the fact, but I agreed to make payment arrangements which were accepted. A few months later in February, I received a letter from an independent mediator at the local courts here in St. Louis stating that a lawsuit was filed against me and that I will be getting served and to call them to discuss my case. I was baffled because the representative with PFR told me that if I made arrangements that the lawsuit would not be filed. I contacted PFR legal department and everyone there acted as if they were shocked that the lawsuit had gone through and that they would call the clerk at the court and have the case taken off of the docket. Well, that never happended. When I talked to the person who I originally set up the payment arrangements with, she told me since I couldn't come up with the full amount of the initial down payment which was $374.27 that the lawsuit was filed. I can't believe they would pursue the lawsuit because $74.27 could not be paid. My initial payment to them was $300 and they agreed to break up the $74.27 into two payments along with my monthly payments of $142.58. I've made 3 payments to them so far which has totaled over $600. I have not been served with a summons from these "zombie" collectors, but the first court date has since passed and there is a new court date. I'm waiting to get served and to also consult with an attorney. I'm just confused. Should I discontinue making payments to these idiots since they didn't hold up their end of the agreement and filed the lawsuit anyway? What should I do?