negative Credit reporting

I have two credit cards from the same lender on my account with the same amount with two different account numbers. The problem is I only had one card with the company and I paid it off. however , One says I paid it off the other says it was transferrd to a collection agency. I called the original credit granter and asked if I ever had two account with them and if they could give me the account number. They stated that I only had one account and that they could not give me the account number because the agency had it. I then called the agency. They claim I made payments. on the debt they have. I know I never did. I asked if they could send me how the payment was made they stated they never had that imformation. What can I do , because both the original credit grantor and the agency are reporting the amount on my credit report negatively. I disputed the information, with no success.