Signed up for the 600 Mbps plan, we have the Arris SB8200 and a Netgear R6220 router. On a good day, I may get between 150 and 200 Mbps down and between 15 and 18 Mbps up. Connect laptop directly to modem to bypass the router, but same result. Any suggestions?
Try calling 1-800-comcast and ask a rep to completely remove the modem from your account and to "re-provision" it from scratch. Also ask them to confirm that the provisioning and account data in their database is correct and complete and that the correct configuration / bootfile for your subscribed to speed tier is being pushed to the modem.