The attorney may or may not qualify as a debt collector, which depends upon whether or not their duties are primarily collection of debts or their primary duties are legal representation, but that is not determinative of ultimate reporting of payments made.
They are an agent of the creditor, so they are responsible for notice to the creditor whenever payments are made.
FCRA 623(a)(2) places the obligation on any party who has reported information to a CRA to "promptly" update that information as necessary to maintain its current accuracy. Thus, as payments are made and notice provided to the creditor, they (the creditor) is then required to update the current balance. No explicit period in days or weeks is set under section 623(a)(2). The legal standard is that update by prompt, which reasonably would mean within their next regular reporting period.
The fact that the account has been charged-off is irrelevant to reporting of current balance, as the full debt remains due after taking/reporting of a charge-off. The relevant factor is the requirment to promptly report changes to the CRA.
If the creditor is not providing updates of the current balance to the CRA as you pay down the debt, then I would wait at least a month and a half after they receive payment. If they have not then reported an update, you could reasonably at that point file a dispute asserting lack of prompt update, as mandated under section 623(a)(2).
As an aside, if the creditor also has a judgment, then they are required under the Rules of Civil Procedure for your state to notify the court within x-days of complete repayment of the debt that it is now discharged. That is not optional on the part of the attorney, and once done, would also be clear basis for proof that the debt balance on their reporting with the CRA should also show $0.
