Credit record damage

I had an Edgars account which was sold to the nimble group. I am now trying to fix my credit record and went into a payment plan in August to start paying the debt and my credit score then was sitting on 610. Since they started debiting in August they have been updating my credit record with the beurea as missed payments and it has dropped to a whole 580. I communicated with them via email in end of September and was promised that it will be corrected only for the month of October to be a missed payment as well. If you debit gets sold to them never ever pay. They will make you credit record even worst.