my modem boxes no longer work, one not at all the other one frequently breaks up into pixels. I want to exchange them
You probably should call Verizon with this request to get a timely response. This is a peer-to-peer forum and Verizon does not always respond.
I believe that when you say "modem boxes", you are probably referring to your Set Top Boxes (medium-sized black or gray boxes near your TVs). There are a variety of things that can be done to troubleshoot the issue. However if you are set on just getting them replaced, PJL is correct about needing to contact Verizon directly. If the problem is in the STBs, then replacement will cure it. If the problem is in the wiring or elsewhere, replacement will not help. 1(800)VERIZON