Mermaid,
I get the "warranty" calls from time to time. Our cars are all way past the warranty phase, so my guess is that these are just another scam - they get your name, your address, your CC info, etc.
You get to call the CC company to let them know that your info was stolen and there are purchases on your card that you didn't make.
These 'offers' occasionally come via the US mail, too, but not from the dealer who sold you the car. The only way to answer those mails is to tear them up and toss them in the garbage.