Unathorized Sale of Materials

I received a cease and desist letter from a review center I enrolled in because I gave my account access to someone else, as I was no longer using it regularly. I didn't do it for profit or with malicious intent—I just wanted the high-quality resources to be used rather than wasted. Now they’re demanding that I write an assurance letter and travel across the country to personally apologize. This is my first time experiencing something like this. What should I do?