The next time they call, demand the name of the company along with a legitimate, physical mailing address in which to send a cease communication letter VIA certified mail with return receipt requested. If they refuse, let them know you will be seeking legal counsel who will get the information for you and will be filing a lawsuit against them for harassing a non-debtor.
Possibly Card Member Services or Discover Account Services, but I do not answer when I don't recognize the number.
Been harassed by this scam group for years now. The only way to stop them is to continue to report them to the FTC/DNC/FBI, etc. If you answer (especially if it's a known scam number), they will continue to call you, possibly 4-5 times a day (this happened today after not responding to them for around 2 years).
Do NOT give them your information, they use phishing techniques to get your personal information such as name, address, and credit card number.