Fraudulent company spamming auto trader ads, lying about having buyers and financing, calls again and again, will not stop calling, refuses to maintain an internal do not call list, calls numbers registered with the National Do Not Call List. I have asked this company repeatedly to put my number on their internal Do Not Call List. They state they do NOT maintain one. This company has called me over 70 times in the past 6 months and will not quit calling even though I have told them repeatedly to quit calling me and put me on a do not call list.
The DNC and other telemarketing rules, unfortunately, do not apply to businesses. However, there are devices you can purchase which will block callers on a landline. My cell phone comes with the ability to block callers, and for those that don't, there are apps that can do it. They may or may not do anything, but you could complain to the FCC and FTC. If enough other people complain, they may take action. I don't know what "enough" other people constitutes. I know it's frustrating, and I'm sorry there is little we can do about it, because I occasionally have the same problem, only with home phones. Hopefully, by now they have stopped bothering you.