pay off

You should first ask the debt collector to validate the debt in order to find out whether or not they own your debt account. If they are able to validate the debt, you can sign an agreement with them that they would report the debt account as paid once you pay off the account in full. Once they are ready to do so, you can start making the payments.

Charge off is an accounting term meaning a debt has been charged off the good books and into the bad. Unless you paid the debt off, you still owe it. You wont get it to show as paid until you fork up the cash or settle the debt.

My question is, what are you trying to accomplish?
Paying the debt alone wont improve your credit score, as FICO scores the delinquencies and derogs that occur along the way, not the payment of the debt. If FICO score increase is your primary goal, you must do more than just pay. You must get earlier deletion of the reported derogs and delinquencies, such as by making PFD offers. But PFD offers require no response or acceptance, so the debt may still just linger.

Delinquencies can mature into charge-offs or collections, and ultimately result in legal action. Reliance on PFDs may result in escalation of their reporting or initiation of legal action. If your primary goal is to stop the hemmoraging now, then a simple PIF may be preferable, with the later use of GW letters to address CR deletion.

There is no one single answer. A lot depends upon what you are willing to risk vs what you seek.