Charged 100$ installation fee after a technician fixing Xfinity network dropping speed

Dear Xfinity, about one and a half month ago an apartment complex where I currently live switched from a residential to bulk Xfinity service using Onboard as an intermediary. I emphasize that there were no warnings pertinent to the change of equipment or other hardware related actions that must be performed on my side due to the service switch. Shortly after that my home devices started to experience problems with the network connection, namely intermittent drops in Internet speed. I requested help from the Xfinity chat bot assistant, however, the problem had not been resolved, resulting in scheduling a technician visit. It is worth noting that there was no mention about any cost when I was scheduling the visit. The technician identified the problem, that it was an old gateway incompatible with a new service and replaced it with a new one. After receiving my December statement, I was surprised to find that 100$ installation fee was included. I draw your attention that it was a problem of Xfinity’s equipment that led to network connectivity issues, and according to the company policy there is no fee associated with the service if the problem due to the Comcast equipment. Simply changing the gateway would be no problem for me if I had been told so, as I already had done that in the past setting up my account. I would like Xfinity to reconsider its decision to charge me, as it was its fault to provide me with a good connection or notify about the need of changing the equipment.