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If the OC has sold the debt, they are done with you regarding satisfaction of the debt. They cannot accept payment.
They have already reported $0 debt due to them. To get the CO itself deleted from your CR would require GW letters to them.
The debt exists, regardless of whether they have reported to the CRAs. They can report at any time.
You have three basic options. You can just PIF today, and the debt will be satisfied. You can try to negotiate a settlement with them for less than the full debt.
Option three is to make a them an offer to pay in exchange for their agreement either to delete any credit reporting, or if they have not yet reported, their agreement not to report.
If time is not critical, it is best to try the pay for not reporting route first.