I cant log into my CM1150v modem

[JTMC123]

Hi, 

I have had the CM1150v for a long time and at the beginning i noticed little to no problems with the modem. With Xfinity I have a plan that is supposed to get up to 800mbps down. At the begining we never really got that, even with a wired connection into the router we only got upto 400ish mbps. A year has gone by and now we get around 50mbps which is not that great considering everyone in my family works from home because of Covid. I called the xfinity guy and he was little to no help and he said that I needed to log into my modem and try to maybe increase the bandwith. I then took a look at the back and went to the web browser https://192.168.100.1 and it says I can't conect to it. I dont know why but I can't. We are thinking about just switching modems or moving to the xfinity xfi rented router. If anyone can help that would be great!

[FURRYe38]

So factory reset the CM modem and connect 1 wired PC to WAN port #1, with the coax cable disconnected from the back of the modem. Can you log in to the modems web page at 192.168.100.1 then with a web browser? Should be able too... 

If you can, then connect the coax cable to the modem. 

Theres not adjustments in the modem to change for bandwdith. Is all automatic. 

Be sure to disable LAG on the modem if you get in.

Please post a copy and paste of the modems connection status page.
Have the ISP check the signal and line quality UP to the modem. Be sure the ISP provisions the modem correctly.
Be sure there are no coax cable line splitters in the between the modem and ISP service box. 
Be sure your using good quality RG6 coax cable up to the modem. 
Be sure to power OFF the modem for 1 minute them back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Mod...