I'm having issues with the Ethernet service on my unit. The box has to be restarted then it works for a short time before they are turned off, Comcast said it was because I am using all 4 ports at once
What is the make and model of the modem?
Box provided by Comcast and is the second refurb replacement
I had that model (XB3) and I was able to use all the etherenet connections. The user manual mentions four ports:
Maybe they thought you have the XB6? It only has two ethernet ports.