The fact that the debt was charged-off is immaterial to the consumer's continued obligation for the entire debt.
As for accrual of any charges, the statutory restriction is set forth in FDCPA 808(1), which makes it a violation for a debt collector to attempt to collect any amount that is either not expressly authoriized in the account agreement that created the debt, or otherwise permitted by law.
That section is also the basis for case law holding that a consumer can include a request for itemization of a debt in a DV, as it is the only way a consumer can evaluate whether the amount of an asserted debt is authorized.
You first step is to dig out a copy of your account agreement with the OC, and determine what amounts were specifically authorized in that agreement as amounts above that of the principal debt. If not specifically authorized in that agreement, then they would need some statutory provision of your state code authorizing a debt collector to charge such amounts above any authorization in your account agreement.
