ATG Credit LLC Screwed my credit Chicago Illinois

I received an e-mail from two of the credit bureaus saying that I have negative information posted to my credit.  A major derogatory account for $159.00.  Please note that Equifax has posted this on their report three times.  Experian posted this on their credit report once.     

I had no knowledge of this debt prior to getting the e-mail from the credit bureau.  If I had known I would have just paid it off avoiding it going to my credit.  The issue now, is my credit score has dropped dramatically and I still don’t know what this debt is about except for it being referenced as a medical bill of some sort.