How did you book the cooking class? How long does it take and what is the cost?
We booked a cooking class on line. Google “Cooking at Home Thai Culinary School.” The website describes the different days and times of 3 different themed classes. You book the class by email to the owner/operators. They generally will have an opening with short notice. You can pay in advance with PayPal and the cost was quite reasonable at ~ $40/person. Plus you get a meal you cook yourself and may be the best Thai meal you’ll have while in Thailand. They come to your hotel and pick you up and return you afterwards. We did a morning class with pick up at 8:45 and return at 1:30 PM.
Get an answer from De Naga Hotel staff and past guests.