A "charge off" is only an accounting entry that removes the account from the preforming loans column to the bad-debt column on the books of the bank. Nothing more than that. The debt is still owed and can be collected after it has been charged off.
However, just because the debt can still be collected does not mean that you should pay the debt collector. Debt collectors are notorious liars. They will tell you all sorts of things (mostly lies) to get you to pay them. There are many defenses to credit card debts, especially after the account has been sold to a debt scavenger. If you receive debt collection calls or letters, you can send the debt collector a cease and desist letter to stop them from contacting you further.
"Charge off" generally refers to taking a loss for tax purposes. If the credit card company sold the debt to a collection agency or vulture fund for a loss, then the credit card company "charges off" their loss, but that does not change your liability on the underlying debt and the purchaser of the debt, so long as assignment of right to collect was allowed per your credit card debt (always is), then collection company can still come after you.
Great answer by attorney Kane. There are debt collection companies out there who actually buy volumes of bad debt from companies for pennies on the dollar, knowing that they can make a few bucks on one or two of the accounts. So, even though the original lender has written off the debt, that does not relieve you of your contractual obligation to pay, and that is why the "vultures" can continue to go after you.
In a bankruptcy, you indicate the addresses of the original lender and also any and all subsequent "vultures" on the bankruptcy schedules and creditor matrix, and then the entire debt is finally discharged, if you are otherwise eligible for the discharge.
This answer is provided for informational purposes only. Actual legal advice can only be provided in an office consultation by an attorney licensed in your jurisdiction, with experience in the area of law in which your concern lies.