Blocking Youtube on Arris XB6 Gateway

I have tried using the parental controls to block youtube but it isn't working. I have searched your forum for solutions, and although it seems I am certainly not the first customer to ask, the only responses I see from Xfinity are non-answers pointing customers to the parental controls which do not work. On top of that, you also have the DNS settings locked so I cant use a service like openDNS to solve the issue. Is there a way to block access to youtube from all devices connected to the gateway or not?