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If the creditor has sold the debt to a debt collector, then yes, they were required to have promptly updated the debt balance owed to them to $0.
If that is the case, then they cannot accept any payment, as you no longer owe them a debt. Any billing statement would only reflect the amount of the principal that was preveiously owed to them, and would not be basis for the consumer being able to send any payment to them.
Having failed to update the balance on their account to $0 would not require the deletion of the CO or of other info reported on the account. The dispute would only require correction of that specific item of information.
Presence of a debt collector could lead to that debt collector reporting their collection.
I would request the name of the debt collector and make provisions to pay them before they report a collection.