Lagging speed and stability issues

I have called and got a couple of techs to come out to check the issue I’m having and nothing changed until one tech came out here and ran a brand new line and told me if I had any problems it’s the modem which I ended up taking back to cox and switching it out I’ve played hardwired and WiFi sometimes WiFi is more stable than hardwired it’s only an issues for my brand new game system so it has to be on the cox side help me please maybe I’m in a congested area which it why I’m getting bad signal while gaming idk but I need help