Speedtest shows very slow, Xinity App shows non-activated modem

I am a director of IT.  I kind of know what I am doing.  I am paying for gigabit service, which worked for a month.  For the past two months it has been very, very slow - 200 Mb.  No amount of rebooting helps.   No amount of AI help works.  I cannot get a person on the line so I have not been able to resolve this.  When they do reach out to my modem they drop service and I am out.  Again, no way to get anyone on a call.   I activated the modem months ago.  I do not understand how Xfinity can be in business still.  What can I do to get through to someone that I am not getting the service I am paying for - really?