Please Help Comcast Advanced Security

Does anyone know how to reach a higher tier tech at comcast? I am having issues when trying to connect to a website while using comcast rented equipment only. I have tested at a location by placing the comcast gateway in bridge mode and connecting my own router behind the comcast bridged gateway and I can connect to the website. If I use the gateway router combo provided by comcast only I am not able to access the website. I did notice that when placing the gateway into bridge mode my public IP address was changed. I need to talk to someone at comcast that understands what security filtering they are doing on their end to determine what I may need to change on the website that I am trying to connect to. Everytime I call I get told I cannot speak to anyone else. They are even willing to cancel all of my service without reaching out to me.