Poor internet quality and consistency. Not getting what I pay for.

For several months now I am constantly getting buffering on numerous devices both via wifi and hardwired. Sometimes the signal drops completely and I get kicked from gaming, streaming, etc. Have reset modem and gateway soo many times and contacted support for refresh signals several others. Still cannot get a reliable and stable connection. I pay for the highest tier of internet and cable xfinity offers which is 1200 mbps and consistently at best get around 290-300 of that with upload speeds of less than 1 on half a dozen speed tests a day. It has caused several meeting failures and more server disconnections for gaming than I can even count. How can I get this issue resolved for once so I actually get the $300/month worth of services I pay for? I've seen posts regarding poor equipment being used by xfinity in particular the cable splitter but am unsure if thats the actual issue. I've had the same level of service for about 6-1/2 years now and up until the last 6 months or so everything was fine. Now its a constant battle and struggle. I'm sick of being told the refresh or and reboot will fix the issue when time and time again it hasnt so I'm done calling support as they seem to have no other tools to solve the problem. HELP!!!!!!!!!