National Dealer Services review: unsolicited calls

I continue to get these irritating phone solicitations from National Dealer Services to extend my cars vehicle warranty. I have asked to be placed on the do not call list, but that doesn't work. I block calls from the numbers soliciting to extend my warranty, but I get a repeat call from a different number ranging from out of state calls to local numbers. The number that called today shows coming from Hattiesburg, MS [protected]. When I asked for the information about the company they hung up on me. I tried calling the number back, and I got a message the number has been disconnected.