Throttling internet

I am curious about this. I am getting 2mbps down and 20mbps up as of midnight before Thanksgiving (when there is a lot of football on). This household is on a grandfathered Xfinity Triple Play plan—much cheaper than any plan Comcast offers today—and when I chatted with the agent, I was relentlessly upsold on plans that I had no interest in switching to as they cost two to three times as much per month. Interestingly, I was running speed tests the whole time I was on the chat, and while the agent was running diagnostics on the Xfinity-provided modem/router, speeds were close to 500mbps (normal).  That was on the mesh the household uses connected to the Xfinity modem through a router. When the agent was done with diagnostics, the speeds dropped back to 2mbps. I have no good explanation except throttling. 

Dear Xfinity rep: I can assure you that whatever it is that you refuse to call "throttling" which results in slow upload and download speeds, IS happening, and it's an issue you need to resolve. Contact your technicians, whoever you need to contact, and stop messing with our upload and download speed. Would you rather all of your customers bail on you for fiber internet from another provider? That's what's going to happen if you don't stop [Edited: "Inflammatory"] your own customers. Enough is enough!