When I answered I got dead silence.

This same person keeps calling but always with a different phone number. So if I block one number, he calls again using a different phone number. How are they able to do this?

They are call centers in Mexico and India that use internet to route the calls to the US which then perform the calls with forged numbers.

the number just called

CALLING ANG HANGING UP SECOND RING, NOT LEAVING VOICEMAIL,2ND TIME TODAY