While a notarized bill of sale may not be needed, other things are often needed. When collection companies try to collect on a charged off debt or paid off debt or a debt that has exceeded the statute of limitations, the collection company can often extend the statute of limitations to collect on the debt if the debtor affirms the debt. So, do not affirm the debt and do not speak with the collection company. Immediately purchase your credit reports from all three agencies (I believe you get one from each free per year). Take these and review and see if this debt shows up by the collection company or original creditor. Write a letter to each of the reporting agencies (each website will tell you how to dispute a charge with that agency) and dispute the charge. Show that it was charged off and you are no longer liable for it, especially if this is a debt from many years ago. But understand a charge off often simply means the original creditor charged it off its books and sold it to a collection agency to collect.