Connection keeps dropping

I’m having an issue where my internet connection keeps dropping out. Seems like every time I go to stream a video on my TV it kicks me out after a few minutes. I’ve chatted with Xfinity agents several times and they always say the same thing. They restart the thing and tell me to unplug it and plug it back in and tighten all the cords, when I know it isn’t going to work because it never does. Then they always want to send a tech over. I don’t want to have a tech over in a pandemic. The last time the guy showed up the internet miraculously returned while he was here and he couldn’t find anything wrong with it. He gave us a new modem but after a few months the issue is back. Why can’t a large company like Xfinity make a modem that actually works? All I want is what I paid for. Would buying my own modem help? I’m caught in an endless loop here and I’m getting really annoyed. There must be a way to get reliable internet with constantly losing connection.