Cox Technician Visit was promised for free but additional service to bill of $100

I contacted customer service to request that someone restart my modem (which was already in my home) because we couldn't restart it over the phone.  Since I believed it was their responsibility to help me restart it, I asked the representative if the visit would be free, and they confirmed that it would be. However, I found out today, the service charge added to my bill, and no one is willing to correct it. This feels misleading, almost like a bait-and-switch. How can I dispute these charges or request a review of the recorded phone call where I was told the visit would be free? I was also told by the nice gentleman (technician) that the visit was free. I never signed anything as well. 

Thank you!