internet speed not being delivered

I am paying for a 1200 Mbps plan and Comcast speed tests (wired, connected directly to router) lately have never exceeded 540 Mbps. More typical is 460-490 Mbps. This is without other devices using any significant data, after rebooting the modem, and so on.

I realize my modem cannot handle 1200 -- it tops out at 850 or 950 -- but it was the fastest Comcast-certified one available when I switched to higher speeds. (It is a DOCSIS 3.1 modem.) When the new service was first put into place, speed tests showed close to 1000 Mbps. Now, they show less than half.

Please fix this!

P.S. What is wrong with the Web page? It has a huge photo and the rest of it is off screen, with no scroll bars, unless I reduce to 50% magnification.

P.P.S. It is annoying to see a letter from your director of customer experience, saying Comcast is customer focussed, and at the same time have all ways to contact a human directly removed from the support Web page. It is bad enough to reduce customer service, but please don't brag about your commitment to customers at the same time!