I wasn't home when the call came in. Caller ID said "Private Caller." I once went through a car wash and was accosted by someone wanting to replace my windshield. The windshield was cracked so I had them do it. Good service, insurance covered it, etc. However I continued to hear from the company regularly, as though they expected me to need a new windshield every month. When I got caller ID, I quit answering their calls. Maybe they switched to "Private caller" because people like me weren't answering their many, many calls. Just a thought.
The best way to stop this call is to pick up the call and let them know that, you have already sold the car and you dont have the car with you anymore. It worked for me.