On your cell, look under Tools, find Security, select the option to BLOCK all numbers/calls except the number call or you wish to receive. I am with Verizon and this option blocks all calls not on my call cells call list. Good luck.
I've been getting these calls at least 10 times a week. When I have time I wait, get connected and "mo fo" them. I know it's a waste of time but I find it enjoyable.