Complaint against an agent

Who do i need to speak with to lodge a complaint about an xfinity agent. The agent was terribly unprofessional. I requested a service to be removed and had to restate my intent 4 or 5 times. The agent was too busy trying to up sale me instead of addressing my concern. Then the agent abruptly ended the chat without confirming a resolution and meeting all of my concern. The conversation started great but that agent's aggressive manner to get me to try something else absolutely ruined the chat and made me question if I should even continue with xfinity after being a customer for over 20yrs. She needs to be restrained and educated about customer service.