Internet drops constantly

A few months back we “upgraded” our internet for alleged faster speeds, the tech came out and installed an xfinity gateway rather than our previous modem/ router setup saying it would have faster speeds blah blah blah. Since then we have had nothing but problems with our internet and when I went try and find the modem and router to get rid of this god awful gateway I all of a sudden can’t find them, my best guess is xfinity took them when switching it out, that’s beside the point. My issue is that everytime you try to load a non google website or load a game and connect to servers the entire internet drops and I have to flush the dns, register the dns, release IP and renew ip to get the website or game to load again, all while google and YouTube work fine, if I try to load a website while in a game it happens all over again, these problems shouldn’t exist for the amount of money we pay for “high speed internet”, we’ve had multiple techs come out and do nothing to help us but recreate a new network that literally did nothing just before rushing out the door