You fail to understand the meaning of charged off.
Charged off is an accounting term that means that your debt no longer falls into the "Accounts receivable" bucket, and instead falls into the "bad debt" bucket. So the business takes a loss on their taxes because your debt is no longer good enough to be considered an asset.
This does NOT mean you don't owe them the money! it means that if they do collect the money, then it is considered revenue for tax purposes.
Collection agencies may be working for the original creditor or they may have bought your debt. Since you are known as a deadbeat to the company, the collecion agency probably only paid pennies on the dollar for the debt. BUT YOU STILL LEGALLY OWE THEM THE ENTIRE AMOUNT.