False Charges to a closed account led to collections

Directv failed to close the billing cycle on a cancelled account after a family move to a new house. Instead of transferring the account to the new address, the representative created a brand new account number. Directv continued to bill my account for 6 months after cancellation and not once sent a notice to my residence regarding a past due amount. This resulted in the false debt being handed over to a collections agency which has negatively impacted my credit. After harassment and many hours on the phone with both Directv and Credence Resource Management LLC, the claim was deemed to be false. Who can I speak with to fix the mistakes made by Directv and repair my credit score?