Upgraded to 1gbs but only getting 450mbs..

I upgraded to 1gbs about two months ago. I have an Arris SBG8300. Went through all the troubleshooting guides and still the same even though I'm hard wired. Thinking it was my modem I bought an Arris SB8200 and also the google wifi mesh system. Still the same thing.. im hard wired. Technician came out to my house and checked everything and said everything looked good. He hooked up his own device and still only getting around 450 mbs hard wired. He said he was going to let his field supervisor know that way I can get a "Network Technician" out to my house. After a week later and a couple of phone calls on my end, still no response from Comcast/xfinity. Can someone please help??