C7000v2 internet slow or cutting out with wired and wireless connections

[dalsamsam]

Recently, my WiFi has been slow and cuts out relatively often, so of course I contacted Comcast Xfinity, my internet provider. They were able to do a system reset and the internet works better for now... but we seem to do this every few weeks! When I pressed further to figure out why this was happening so often, the Xfinity representative said the following: 

"It it likely the settings of the modem itself and you should contact the manufacturer of your modem. Please ensure them that we did check it already and the internet service on our end has no issues at this time. I am confident that the repeated issue has something to do with the settings of the modem that needs to be corrected by your manufacturer since we cannot access that on our end." 

The repeated slow internet speeds/cutting out happens on all of our devices (phones, laptops, PC computers) and happens whether wireless or wired via an ethernet cable. 

Any thoughts? I can't get direct support from NetGear without paying them a hefty sum so really crossing my fingers someone can help on here! 

[FURRYe38]

Has a factory reset and setup from scratch been performed since last FW update? 

Any Wifi Neighbors near by? If so, how many?

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...

[dalsamsam]

The modem was purhcased new a few months ago--I set it up then and have not done any factory reset or set up from scratch since then. I wouldn't know how to do that if it was necessary. How often is this needed and can you point me to a resource that shows how?

Yes, tons of WiFi neighbors. I live in an apartment in Boston MA, no way around that.  

ISP has assured me it has nothing to do with them. 

I have no way of seeing or changing if there are line splitters. I live in an apartment. 

COAX cable I'm using in my apartment is brand new and tightened in place. 

The modem has been powered off and back on multiple times while trying to solve this. 

From this further info, anything you can think of? 

[FURRYe38]

Is there a button on the modem to disable wifi by chance? If you have lots of other wifi neighbors around you maybe experiencing some interferences from nieghboring wifi signals. 

Might see if you have a power setting for wifi Under Advanced Tab/Advanced Settings/Wireless Settings

Try setting manual channel 1, 6 or 11 on 2.4Ghz and 40 to 165 channel on 5Ghz.

In back there is a small recessed button. Press this button for 10-15 seconds then release. Might try this later on though.