Messed up my credit score

I had an edgars account with a balance of 600+- on it. When edgars was going through its trouble it sold my account to nimble. My installment was 70 per month. I had difficulty paying the account cos edgars was unable to find it on the system. Eventually I managed to pay it in full, but I now I see they have updated my credit report that I missed a payment with them in December and I lost 18 points on my credit score. I don’t owe anything and I paid my account in full. Don’t like how my credit report gets tarnished for such a small amount.