If the charges were truly not disclosed--the information about them was not available to you--prior to or at the time you agreed to the take the course, they cannot retroactively add a charge. However, if information about the charge *was* available, but it's simply that you did not notice that charge, then you may be obligated to pay it; so, for example, if the costs were reflected in the course brochure, the paperwork you signed to take it, etc., then you probably have to pay them even if they were not specifically called out to you. You say that the charges were only "brought to my attention" after the course was completed; if this means the information was available, but you simply weren't aware of it, then unless the information was so confusing or well-hidden the average person couldn't have become aware of it, you likely have to pay.