TV will not connect to WIFI

One of our tv’s will not connect to the WiFi. Technician was out here on Jan 7th and told us our gateway modem and tv boxes needed to be replaced. He went out to his truck and replaced the gateway, but he could not get the tv in question connected to wifi and ordered 2 tv boxes.  He said it was easy to connect the tv boxes but also said if we had trouble to each out to him and he would come back to our place and do it for us. Well the boxes came and we tried to connect the tv to WiFi but it would not connect. Called xfinity to help 3 TImes at least over the next week, and NO one could help to get this connected. Have no faith that they can get this done. Supposedly a technician is coming to our place to get this rectified tonight. Does anyone have any feedback here that may shed some light as to what the issue may be… really unsatisfied consumer here