Hello JK27571
SB6183 is a cable modem and can provide above 500Mbps speed so you can access internet on direct connection with the optimal speed according to your speed plan and the firmware is part of the provisioning and is pushed by the ISP. Nothing the end user can update.
Whenever a tech from an ISP says a modem needs a firmware update and to contact the manufacturer, they’re just trying to get you off the line or they don’t know what they’re doing so don’t trust anything they say.
They know the firmware is part of the provisioning when the setup the modem. Its pushed by the ISP.
The 250mbps, is that the speed directly connected to the modem or through the router?