debt collectors often try to pressurize you by making you pay on some non existent debt. This debt can even become legal and you will have to pay for it.
collection agencies doing illegal business will purchase charged off or time barred debts and start contacting you. Suppose they call you for a debt of $10,000 which you don't owe. They will frame it in such a way and making you think that you owe this debt.
You think of ignoring this call as it is a charged off debt and is not shown in your credit report.