I am in the process of doing this. You should call the OC and see if they still own the account. If they do, ask them if you can work it out with them. If you pay them, the CA doesn't have anything to report. Get in writing from the OC that they will contact the CA and get them to stop reporting and take it off your report.
Don't dispute the CRA's. Once the debts are PIF through the OC, then DV the CA if they are still reporting. Since they won't be able to validate, they cannot report. You can also have the OC write a letter to the CRA's for you stating that the accounts are paid and should not be reporting. I believe that to be correct. I am sure that if I am wrong, someone will let us know.
GL.