I have been on the phone with Xfinity support for two hours, on phone/chat, and via facebook portal. We have a Netgear CM700, and since we've gotten service with Comcast(July '19), we've had terrible speeds(125 down average, paying for 600). We've had a technician come out and troubleshoot, and we were told the issue lies with our modem. I hopped onto the modem portal, and realize our modem's firmware is out of date. We keep getting told that Comcast cannot update firmware, despite that not being the case. Can anyone help? It's just a simple firmware update.
According to Netgear Support, https://kb.netgear.com/000036375/What-s-the-latest-firmware-version-of-my-NETGEAR-cable-modem-or-mod... you cannot update the firmware yoursel, but your ISP has to (document updated 11/13/2019). That link provides the Comcast Deployed version. If you think you don't have the latest, maybe Comcast isn't ready to support Netgear's latest, but only what they have provided?