Reporting sold debt
Your account has been charged off. It will appear on your credit
Your account has been charged off. It will appear on your credit report for 7 years. Any negative item will appear on your credit report for 7 years. There is nothing illegal about it.
When the OC charges off your account, it means they are writing
When the OC charges off your account, it means they are writing it off as a bad debt/loss and therefore they report it to the CRAs. The OCs have the option of 'selling' off the debt to a collection agency for a fraction of what its worth or they can also contract a collection agency to collect the debt on their behalf. In your case, the debt has been written off and then sold. The OC reported it since it appears as an item of loss in their books.
Is the debt valid?
Yes the original creditor can report it to the CRA's and it will stay on your reports for the next 7 years. That's legal. As for the CA reporting it to CRA's...that may vary depending on your situation. First off, did you send the CA a validation letter within 30 days of receiving their letter?