Charged $100 without Prior Notice or Consent

Last month I signed up for Xfinity Internet and elected to do self-installation for the modem. At first I wasn't able to connect my device because the Xfinity app wouldn't recognize that my phone had an Internet connection through Mobile data. I got on the phone with Xfinity tech support, and they ran me through the connection process remotely multiple times and were still unable to get me connected. They said that a technician would need to come out and fix it manually. At no point was I told there would be a charge associated with this visit, so I agreed. The technician came out and said that the coaxial cable i was using wasn't working, and that another one in my apartment should have been able to connect. I had tried every cable in the apartment multiple times and told him that. He was able to switch the active cable to the main one I had been attempting to use, and I was then able to get WiFi. Again, at no point while talking to him did he say I would be charged for the visit. Now it's a month later and I've received a $100 charge for the visit out of nowhere. I'd like to be able to recommend this service l, but so far my experience has been negative and felt predatory, and I'm inclined to look for another internet provider when I get the opportunity.