Intermittent internet service for the past three years!!!

I am extremely frustrated and upset with my xfinity service, and lack of knowledge regarding my problem.  We constantly have internet dropping issues and intermitten levels of upload/download speeds.  

 

During the first two years of service we complained and complained, comcast swapped out modem after modem to find no fix.   They even upgraded us to 500 mbps.  The problem continued.

 

Then we decided to buy our own equipment, and bought on the higher end.  Netgear CM1000 modem and Netgear Nighthawk router.  Still same issues.  Streaming shows droppped, devices dropping off the wifi, and speed tests illistrating speeds drastically goin up and down.

 

Then about three or four months ago a tech told us the interior cable was bad.  We called up our electrician and had the cable swapped out.  Seemed to do ok for a week or so, then back to the same problem.  We just had a neighbor move in across the street and had xfinity hooked up...seemed to get even worse after that.

 

I am really disastified with my service that I am paying for, and more over as I dig into this problem and try researching, I see xfinity customers all over having this issue.  What is up with that???  What is the fix???