Getting random ping spikes

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 then back ON.
https://community.netgear.com/t5/Cable-Modems-Routers/General-info-and-Troubleshooting-for-Cable-Modems/m-p/1530376#M12853
https://www.duckware.com/tech/solving-intermittent-cable-modem-issues.html

Netgear has set up a community forum specifically for the Cable Modem products. Might be more likely to find someone who has a solution if the question is posted there:
https://community.netgear.com/t5/Cable-Modems-Routers/bd-p/home-cable-modems-routers

Please use this link to the main forum product list to review and choose where to make your posts. 
https://community.netgear.com/t5/NETGEAR-Forum/ct-p/en-netgear

Thank you.