national credit systems Threatened Me, Disrespectful, Illegal atlanta Georgia

In July of 2013 I was inevidected from my apartment complex. I feel on hard times, single mother of 4 children. Luckily the complex was charging me $1166.00 for fees. I could not pay it, in Oct I spoke with  H. Sanders at National Credit system, and told him I was willing to pay $50.00 until the debt was paid off. He told me to pay $50.00 until income tax and than pay the complete balance than, if not I wouldn't be about to move into a apartment, and this would hit my credit. I told him no. Unfortunetly my son fell ill and I could not make any payments. Today 1/24/14 I receive a call from H.Sanders again, I was already aware that they placed this on my credit report. And he said yes because you didn't pay, now if your tell me that you will make a payment with your income tax in full that we can resolve this. I said no, let it stay on my credit. I called back that same day, after cooling off to make a payment and payment arrangements. Again this H. Sanders proceed to tell me that to make a payment and pay in full for my income taxes and thats all he wanted to hear, if not he would let this stay on my credit until 2023 and begin to threaten me by telling me and forcing me to pay the amount in full. Than I told him it is illegal to make threats in the State of Florida when it comes to collections. I asked to speak with his supervisor and his supervisor literally told me if I tell him something is illegal I have to quote the statute, and I am literally sitting here on the phone with this guy thinking what is this? I told him look is there anyone above you I can speak with. He said no, and added that they will get the money or I can enjoy moving from apartment to apartment, with my 4 children since no one will accept me because of this. Like he is a god. This is unfair pratices. I told him I wanted to make a payment but speak with his supervisor and he hanged up on me. So how can I pay if they refuse to accept payment?