Where can I leave feedback for an employee?

I recently filed a complaint with the FCC and received a call from a resolution specialist. I’ve never felt so belittled on a conversation. I want to provide genuine constructive feedback for the team and person that I talked to. The last thing i want to do is complain about a paying for a service that’s not working but the follow up call left a horrible taste in my mouth. I downgraded my plan today and I’m looking for another provider. Honestly, I called Verizon, t-mobile, phoenix internet, and none of them support my area. 
So because my area is monopolized by COX and my internet goes out, I have no option but to listen to someone talk sarcastically about how they understand how my feelings are hurt. Now I’m ranting on a forum for the first time in my life.