I picked up the phone and no one said anything, but just a tiny click.

I got this call 4 times today trying to give me a great discount on something.  My son took the first call and didn't understand anything so they kept calling back.  I said I wasn't interested and hung up.  The call came again and again and again.  I either don't answer or pick up then hang up but they keep calling.  How do I get rid of them????  They are SO rude.