Im getting calls from a 9 digit number every half hour. how do i get them to stop?

they started calling me around 2 this afternoon and every half hour proceed to call me again. so i picked up once and it was a gentleman who said he is trying to give me a car insurance quote and will i accept people calling me to give me the best quote. i told him to put me on the do not call list but they are still trying to call me. how do i get the calls to stop?