Called and said nothing...

I get calls from this @ twice in 30 miniutes.  I do not answer.....How can I block them?

I have caller block  but that does not always hold. The Reason "they" don't answer - it is a recording , Political.
In FACT THE MESSAGE WAS COURTEOUS. (BUT ARE'NT THEY ALL, IF THEY WANT YOUR VOTE? Whether  R" or D" - I make up my own mind).

Harassing calls all hours of the night