Inconsistent download speed is making participation in on-line Zoom meetings really problematic

I am paying for 1000 mbps download speed.  After having persistent issues with my screen freezing in on-line meetings, Ihave been  using Ookla Speed Test every time before logging into meetings to test my actual download speed.  I have documented a wild and consistent inconsistency that almost every time falls short of the promised 1000 mpbs download speed.  I have three times called and spoken with a Xfinity technician and after the first tech sent me a new modem and an extender, nothing has really changed.  I get a great wifi signal from my home office to the router/modem, but the download/upload speed is all over the map.  I now do consulting from my home office and need a consistent signal.  

How do I get Xfinity to upgrade the service to my neighborhood to assure me that I am getting the level of service I have contracted for?

Lincoln Ferris