4th modem rental from Comcast since March, blocked from my admin portal?

Hi I am hoping to get this straightened out ASAP. I have swopped equipment, because I was told that the previous modems that Comcast gave me were all defects, oddly enough I went with it, and now I cannot get a secure connection on any device in my home. My laptop is resetting itself to 2009, and regardless of what I try it will not allow me to connect to a browser and says that my connection is not secure. Whatever site I attempt to connect to it says that is impersonating EX: Chrome, and attempting to steal all identifying information and shuts down. This happens when I use my tablets, phone, and any device in my home over heats and dies. My smart tv is not connected to my home WiFi, and no one can give me an answer to why this is happening. I have called, reset my device, reset names passwords etc, and I was told that Comcast was going to fix a connection issue outside with upstream/downstream. I cannot login to my admin portal, and obviously that’s a problem.