Just block them....if you have an iphone go to the list of recent callers.....you will see an i to the right of the number....click on that and scroll down.....you will see "block contact"....click on this and they will not be able to call you again....
WARNING--BEWARE!! These callers are B I G credit card criminals, known as the card service scammers! Under NO circumstances, give these lowlifes your credit card number, or you will regret it forever!
just called me and I didn't answer. they are really stupid if they think people will answer a number they don't recognize with all the scams out there anymore.