As for any amount they are attempting to collect, take a peek at FDCPA 808(1), which provides that it is a violation for a debt collector to attempt to collect any amount that was not either specifically authorized in the account agreement that created the debt, or is not otherwise authorized by law.
If any amount is not specifically authorized in your original acccount agreement, then check out your state code for any specific authorization for a debt collector to collect amounts not authorized in the account agreement.
if the answer to both of those investigations is no, they are in violation of section 808(1) for attempting to collect any such amount.