If you had the plastic NAUI Certification card with all the NAUI information on it, that's all you needed. There is no set "standard" for what your C-Card does and does not have to include. Your certification number really means absolutely nothing to a dive shop or resort. It's only real use is for the training agency to track who you are.
The NAUI cards have your name, certification date, the certification level, your instructor's name and instructor number and the name of the facility that did the training. That is all that is required on the NAUI C-Card. The person at the resort simply didn't know what they were talking about.