We owe several hundred dollars to a landscape service, which we are paying off monthly by mutual agreement. Recently, the owner decided to begin charging 10.00 per month, PER LATE INVOICE, in addition to the 19% finance he already charges. Can he do that?! And are we obligated to pay it? At that rate, we will never get the balance paid, at the payment we can afford...not to mention that the balance we thought we were paying off and his now differ significantly. Help!