I was sued but settled out of court but now i still owe what i was being sued for?

I was almost sued by my apartment complex for 7,000$ in back rent and there lawyer contacted via certified letter i contacted him back and said I don't owe this much because i have a letter stating i was living here rent free until a certain time due to it being section 8 this was ok. Shortly after the time where the letter says i need to start paying rent they sent me this letter saying i owed all the rent since i lived there. So i told the lawyer i'm willing to pay 3 months rent because that's all i owed really he then said he would talk to his client and see if that was ok. He called back said it was ok and we would settle out of court and he faxed me some letters saying i only owed 1800$ and it was to be paid by a certain time which hasn't passed yet. Now i'm getting letters in the mail from credit bureaus saying i owe 7100$ to this apartment, but we have an agreement i only owe 1800$.... What steps do i take now in getting this settled. Do i have any valid reasons or ways to sue them now? I would really appreciate some valid answers because the law isn't my forte and I am looking for knowledgeable answers. Thank you for your time in reading this and i appreciate every ones answers and opinions..