pixeling and audio problems

Over the past month I have had constant problems with pixeling, audio cutting in and out and the picture freezing.  I have been through your customer support automated system and talked to a representative, as well as having three technicians out here.  But the problem continues.  I have replaced the original dvr box and one other box but still the problem persists.  The last technician installed a "screen filter" of some kind and that worked for a couple of days.  But the problem came back.  I don't understand why nobody can locate the problem and fix the issue.  At this point if I can't get any assistance, I'm looking at cancelling my xfinity and going to FIOS.