Unreliable Internet -- getting < 10% of the speed that I'm paying for

I have the 1000 Mb plan and my speed test on the best day has been showing 135 Mb. My zoom calls are showing "unstable" and freeze on calls every few minutes. While on calls, I will conduct the speed test and it shows 8-10 Mb -- this is about 1% of what I am paying for.

During these times, I am not streaming any movies, games, or any other activities that would predominantly suck bandwidth. 

How do I get Xfinity to address this? Paying for a gigabit plan and not being able to have a simple video conference call through my laptop is ridiculous.