AmeriCredit/GM Financial Credit Reporting Fraud Arlington, Texas

My ex-wife had a car financed through Americredit and this was a joint account. The car was paid off by insurance after an accident.  My ex-wife had been behind on payments thus Americredit turned it over to collections and placed it on my credit report in 2009.  I contacted collections and agreed to pay 1/2 of the amount owed in exchange for this item being marked paid as agreed on my credit report.  I have documentation supporting everything.  Now, in 2012, GM Financial is reporting the account as being a charge off which is showing up in derogatory information on my credit report.  GM Financial refuses to honor the agreement which was made with AmeriCredit in 2009.  When I call GM Financial they place me on hold for over 45 minutes at a time and just keep saying there is nothing they can do.  Americredit/GM Financial are not interested in reviewing my written proof, although I am sending it to them anyway.  I am reporting them to the Attorney General and anyone else I can come up with, as I have read many stories of the same type regarding fraudulant activities by this company. In short, I need help!  Someone needs to protect honest consumers who really try to keep good credit and pay their bills.