slower than advertised speeds

Hi, I am paying Xfinity for "1.1Gbps" download speeds, however I can never get above 400Mbps, no matter what time of day I run a speed test. I have tried calling the support line and chatting to the assistant bot, nothing helps and I desperately just need to speak to a human now about this. I am connecting directly from the router to a laptop using an ethernet cable with WiFi disabled. I have tried all the different ethernet ports on the router, I have tried different ethernet cables. No matter how many times the chat bot or automated phone assistant remotely reboot my router, the speeds are still way below advertised and I'm getting very frustrated that no help is available! Can someone from Xfinity please reach out to me to help me please?