Call on cell phone. I just don't answer phone numbers I don't recognize. If they don't leave a message than I either don't know them or it's not important. This way I'm not bothered. They usually stop calling. Try this TIP ! haha
Got a call stating they could lower my credit card interest rate, push 1 to accept, 2 to be removed. I pushed 1 and asked what country they were calling from and the foreigner, hung up. He couldn't even speak any English.