Bought a car

I bought a car from R & R that Both Dave and Richard told me ran on both CNG and Gasoline. I took a train from Utah to get the car. They were very nice. Dave told me that they had been driving the car on CNG and Richard guaranteed me "I 300% guarantee you that it runs on CNG" He told me that he had driven the tank empty to ensure all was working. Because of the travel distance and time of day, I didn't have a viable option to go 30 miles to find a CNG station to test it out. Afterall, Richard is a certified mechanic and told me that he personally would guarantee me it ran on CNG. I took the car, and after 12 hours of driving I finally had the opportunity to fill up and drive on CNG... to my shock, the CNG tank was full and the system didn't work. I immediately called Dave and he told me to find a Mechanic to diagnose it and he would take care of it. I found a certified mechanic who diagnosed it as a bad compuvalve. I called Dave back, he now won't take my calls.