I had the same problem. You can block up to 5 phone #'s for free with Verizon.
Go to "My Verizon", then "My Plans and Services", "Manage Verizon Safeguards", then scroll down to the free "Call and Message Blocking".......it's pretty far down on the page, so just keep scrolling.
It requires a 10-digit phone-number; and this is the one you should put to block them 970-002-7588 (it worked for me).
Good luck!! That crap is annoying!