Seller Networks A "We'll sell your car" rip off. Las Vegas Nevada

I was driving down the road one Thursday afternoon with my mind distracted by other problems when I received their phone call offering to do all of these things to sell my car for me. They made it sound great so I gave them my credit card info and accepted their deal. That night I looked at their reviews and saw that it is a scam where the company will take your money and do nothing. I called them the next day, Friday, less than 24 hours later, and told them I wanted to cancel. Was told, "we have already done too much for you to cancel now". (What ever happened to the 3 day buyers remorse clause?) Anyway, I disputed the charge to my Discover card but ultimately learned they had sent Discover some documentation that showed the car was listed on some website somewhere so they had completed their obligation and deserved to be paid. If they did anything, it was totally ineffectual because, over the next almost 3 months, I never received a single indication of interest from a single potential buyer through whatever "super effort" they made. So...all I have for this $210 monetary investment plus several hours of my time, is the wisdom that a person should NEVER answer unsolicited phone calls because they are probably unscrupulous people running some kind of scam. Discover says there is nothing that can be done. They have paid these people and there is apparently nothing that I can do except try to warn other potential victims before they are scammed.