CM1000 and CM3000 not getting appropriate speeds

I'm on a 1200Mbps plan, had a Netgear CM1000 and called in for intermittent drops.  Technician said work had been done recently in my area and my modem was 6 years old, bought a new Netgear CM3000.  I'm only getting 400 Mbps down with either modem.  Had a technician come out, no luck.  Phone support says since my router is customer owned and I have internet access there's nothing they can do.  I've got a wifi router (R7000) coming off the modem.  How do I pull something close to the 1200 Mbps I should be getting?