Charged $100 for 3 min visit

I was having problems connecting to internet which I troubleshooted using the online tools/chat. The system was giving me different answers until it offered to send someone to check on my connection. The service was scheduled for the afternoon but Xfinity tech called me right away asking gif he could come in earlier as he was literally downstairs (I live in a apartment building). He said that it was better to take the device because they couldn't guarantee that the next technician could make it on time so I accepted. I was reluctant at firs because I still wanted to try disconnecting everything (for the second time) and see if my internet was working again. So the tech came in and connected a signal reader and said that I had connectivity. I put everything back together and sure enough my internet was working. He left and never mentioned that I was gone be charged $100 for his visit!!! I just found out when I saw my bill.

I do not think charging the fee is right - first why was the tech able to arrive within 5 min of receiving my appointment confirmation via text which was scheduled later that day? why was there a tech nearby if there wasn't connectivity issues in my neighborhood? why didn't he or chat service mention that I was gona be charged for the visit? I would not have accepted the appointment if I knew they were gonna charge me for the visit.

I do not think this is the right way to do business and think this is unfair to the customer