I feel that you started on the right path. It absolutely makes sence to put money in to a nitrox course instead of just replacing a C-card. In your case you didn't have a choice.Bottom line I lost my NASDS card and was being told no way to get a new one (fire and so on). I used his service and he helped me.
Yes, it was good that they were able to help you. However, upon completing your on-line course did an instructor go over your test?
Did he explain how to analyze a Nitrox cylinder? Did he have you analyze at least two Nitrox cylinders? Did he show you how to set the FO2 on your dive computer? Did he have you set at least three different nitrox mixes on your dive computer?
Did you fully understand Nitrox after your on-line course?