Oil pulling isn't going to do anything for your cavities. Where it really shines is with gum issues/disease. And that's usually the bigger problem for adults.
Personally I'd try another dentist for a second opinion. I've told the story here before about having an aggressive (polite term) dentist growing up that every 3 months put in 3 new fillings. Once all my teeth were filled, he decided they needed to be filled again in other spots.
Years later another dentist looked in my mouth and looked shocked. He said "Do you realize your teeth have multiple fillings?" I asked if they could have been necessary, and he shook his no. At that moment I realized how screwed I (and my parents) had been. Not saying it can't be legit, but I'd at least check it with another dentist.