Force Firmware Update for third party modem.

I have a third party modem. The current firmware is the most recent but I have reason to believe it has been compromised.

I need xfinity to force the update push for the firmware. The staff says "We don't handle the firmware update for third party modems" but that is incorrect.

How can I force xfinity to reinstall the firmware on the modem? I've tried factory reset, that does not re-install the firmware.

I would like to avoid buying a new modem.