Internet keeps cutting out

The subject of this post is Comcast internet service issues. I'm at my wits' end with my Comcast internet service. I've had an ongoing issue with slow and intermittent connectivity. A technician visited about a year ago but the issue never fully resolved. He suggested to purchase a Netgear Modem CAX30S -100N. I was told by him that it was the best modem to solve my issues. I hooked everything up and the internet seemed to be working pretty well for several months. I obtained a ZUMO box from Comcast to stream TV at some point along the way.. Then my issues started all over again. I was on the phone with Comcast for hours trying to resolve the problem of intermittent internet, but I could not get through. Comcast then sent a technician to my house, and they determined that I needed a new line to my house. After waiting 4 weeks for a new line to be installed, everything seemed to be ok. A month later, though, I had the same issue, only this time, there was little to no internet. The tech came back out and said that my signal was strong to the Netgear Modem and that I would need to contact Netgear. After paying $169.00 for technical support and spending 6 hours on the phone, I was still unable to get it to work. They told me it was a Comcast problem. I had enough! I went back to Comcast and got one of their modems, and I was able to return the Netgear modem to Best Buy. I have the fastest speed 1200, a Netgear switch coming off the Modem, and the modem is hooked directly to the ZUMO box. I'm at a loss right now; I am getting over 800 Mbps according to my Xfinity app, but the ZUMO box says there is no internet connection. Does anyone have any ideas?