Where can I complain to the manager of customer service

I booked an appointment to fix my internet problem with an agent on the Xfinity app. The booked time slot is Nov. 29 8-10 am. On the day, I asked for a leave from my work and waited at home from 8 am. After 1 hour, I did not see anyone coming, then I asked the agent on the app when the technician will come, and the agent told me "please be assured the technician will visit, he is delayed, will come in 30 mins". OK, then I continue to wait. After 30 mins, I still did not see anyone. So I asked another agent again, this time the agent told me the technician is on his way, he will come in 15 mins. Alright, I waited again. It was 10 am already, the technician was not coming. So I asked the third agent on the app. This time the agent told me I didn't book an appointment at all. So what was the first agent who I booked an appointment with doing? The most unaccepted are the second and third agents who were confidently told me the tech is on the way... It was really a disappointing experience. I lose my month to ask a leave but the problem remains unsolved. This totally ruined my day.  So I'm asking where can I complain to the manager of customer service.