Tell them the person they're calling is deceased.
In seriousness, you can tell each one that calls that you want added to the no call list, but the problem is while one dealer will honor that, none of the others know that. Your name was either harvested from a central location (likely) or sold for such purposes from either your dealer or their network (also likely). If you supplied your cell phone number with the information, that can lead to cell phone credit/status queries to that provider. If you used a credit card to pay for the service, that can be queried, or more likely, many other shops/stores/chains that all agree to sell information to central repositories can track many of your purchases and habits without even asking your credit card provider, just because all the places you go may share and group that information up front. If you fit whatever profile of spending plenty money on things people with money spend them on, you can come up in searches and whatnot.
Sometimes the call about your car is just a conversation-starter. They're not at all interested in your car. They just using that as an excuse to give you a call/mailing to get your interest and then sell you a new car at their profit. Works better than just calling up and asking if you'd like a new car.
Advertising in the digital information-hoarding age is sneaky.
