If your phone allows you , set the ringer for that number to nothing, at least you won't hear it ring.

What happens when you answer the call and press 1? Eventually it should get you to an option to opt out, or allow you to speak with a person and ask they stop calling you. Calling it back will serve no useful purpose, as they are not calling from that number.

Because they will probably change the number they are showing on a very regular basis, paying to block them would just be silly, they will just call from another fake number.