Netgear CM700 with gigabit internet??

So I just upgraded to gigabit internet and according to the my account info it shows that this modem is compatible with the 1000Mbps internet but customer service is telling me that this modem is NOT since it is DOCSIS 3.0 and Gigabit needs a DOCSIS 3.1 modem. I was getting around 600Mbps down/18up on my previous plan and not im getting 700Mbps down / 6up. Does anyone have any experience with this modem and the gigabit internet plan? Not sure why my upload speed with get cut by 1/3 with the gigabit plan tho.