NetGear CM3000 can not connect

I recently upgrade my plan to 1Gbps, and bought NetGear CM3000 MODEM according to the recommended device list, but it doesn't connect! Had to switch back to the old one.

With CM3000, Xfinity App shows my device stays offline. However the solid white lights on the MODEM (see the attached picture) indicates it's working, according to the manual: "one or more downstream and upstream have been locked, and the modem is online". Any idea what's the problem is? Thanks in advance!