Its a person whose testing your ability to block them, because they are trying to success your phone computer part.its why they keep calling. Best to not answer any number you don't recognize. Let it go to voice mail.
I kept getting these calls also. I finally picked up the phone, waited to hear an actual voice say hello and proceeded to say; you have reached the porno hot line, press 1 for men, 2 for women. They hung up real fast! I don't know why. lol