Formal Complaints and Customer Service Resolution

How do I go about making formal complaints against multiple individuals within xfinity customer service? Also, I need to speak with someone, who can actually help, with resolving an issue with my internet and the time provided that I agreed to with these, so called, customer service people. This doesn’t surprise me, as we all know that Comcast/Xfinity doesn’t truly care about customer service. Otherwise, there wouldn’t be so many complaints.