$100 fee for "free" tech visit

I was having constant slow speeds to the point where the Xfinity app was offering free tech visits. I finally caved in and set up an appointment that I was told over and over it would be free by the customer service member through the chat function on the website, but now Im getting a $100 charge for the visit. The problem ended up being something I had no control over, it being the wiring for the building was faulty and even the tech who came out was appalled by it and how slow our internet was, but now Im faced with an $100 charge. I was also told by the person who had set the appointment up for me that I would to be given a $10 credit for all the issues I was having. I feel very betrayed by the blatant false advertising. Instead of $10 off I was charged for a supposedly free service. I am completely and utterly disappointed.