False Technician Recovery fee of $100

I discovered that I was falsely charged $100 for Technician Recovery a few months back. I got my new Comcast internet in Feb and installed the modem by myself as it was explicitly mentioned that this fee would be waived. Then the internet was poor for a while, which caused me to contact Xfinity for a fix. A technician did contact me about a problem, but it was *not* on my end. No technician ever came to my home to fix any incorrect set up of the modem or wire or anything from my end. Clearly, the technician fixed something on Xfinity's end and then charged me for it. I have already reached out to Xfinity/comcast to provide a detailed work order detailing exactly the steps taken by the technician to fix "any mistake on my end" to justify me being charged for it. I spent more than an hour on calls jumping through multiple customer service agents from Xfinity. Even though Xfinity claimed they would email me a pdf about the technician fix, I have still not received anything even after more than a week. What's the exact procedure to find out more details about this "Technician Recovery", and recover the false charges on my account?