Attorney help please?

I was sued from my old apartment I used to live But a creditor work for them. So I was sued for 3,400. So I started to pay them one Hundred dollar a month after I paid four hundred dollar. They decided to do a garnishment at my employer for 3,700 for $200 intrest $50.00 writ of execution and $50 court fees. So i do agree with that amount. But after the 3,700 was garnished from my employer. I asked the creditor how about the $400 I paid previous and they told me its other fees and i believe that it don't make sense. So my question is can they add other fees in the amout of 400 hundred when they did not even let me know what it was for. What can i do what is the law. Plus its on my credit do they have to removed it or how do i do that do i have to have them give me a some kind of paper work that i paid in full and more. THANK YOU VERY MUCH FOR ANY HELP IT MEANS ALOT SENSE I LOST MY JOB