After a charge off has reached 7 yrs and is no longer on your credit report can a private company bill you for payment on behalf of the creditor?

The answer to your question depends on the laws which govern the debt.

Morally, if you owe a debt that is 7 years or older and have never paid it, you still owe the debt. The 7 year time period is how long the derogatory information may show on your credit report. There is a separate time period, the statute of limitations, for how long you could have been sued over this debt. Both of these have, most likely, expired.