How is it not considered extortion and defamation?

I was hospitalized late last year for a period of 4 months.Due to a lack of income I was eligible for Medicaid.My Medicaid number was given to all parties who treated me after I got out of the hospital.By the time I got around to checking my credit reports there was negative information posted by collection agencies before I even got out of hospital.I've given my number to the worst of all of these companies ACB Receivables Management.They still insist I was not covered when everyone else has already received their payments and refuse to remove the negative information even after I presented them with a letter from NJDHS that claims that I was covered during the time that I was reported for.ACB still insists that I was not covered even though I've given them proof that I was and edicaid covers all of the treatments that I received.Mycredit score has dropped to below 600 and this is the only negative information on my reports.I've disputed with all three bureaus and they will not remove