Pixelation issue

I am having pixelation issues across multiple boxes and channels.  I have tried all the troubleshooting methods through Xfinity assistant and finally got a service appointment scheduled.  The next day I received a text that my appointment is cancelled because some test said my system looks good.  I tried calling the 800 # but can't get a person.  I need a tech to come out and solve the problem.  Please help.