Dispute charge, a home technician visit was a repair not an installation

My internet stopped working. Xfinity phone support said I had a bad modem, so I replaced my customer-owned modem. The internet still did not work. A technician made a home visit. The technician said my modem installation failed so he wanted to charge me an installation charge.  I told him to get it working and we will determine the charges when he found the problem of internet failure. The technician needed to replace an Xfinity-owned "UU" distribution amplifier to get my internet to work. This was a broken Xfinity-owned equipment, not an installation failure. The technician left, and I did not sign or get at the trip report of his service. The technician and I did discuss the amplifier removal with a passive non-powered distribution block. My modern was installed properly but could not work with a bad Xfinity amplifier. I was charged a $100 installation charge on my bill for a simple Xfinity amplifier failure. Please remove the $100 installation charge, it was an Xfinity repair. I would like to see a trip repair ticket for the technician's duties and the parts he used.