Internet Connectivity Still Terrible After Replacing Modem

Hello,  After going back and forth with Xfinity for months, I recently replaced my modem with a Hitron CODA56.  A tech from Xfinity installed it just to make sure that everything was set up correctly.  My internet connection is still horrible, inconsistent and unreliable.  At times it is fine and at other times I simply can’t connect to anything.  I do not know what to do.  I would love to cancel my service but I do not have a lot of options.  Still, I may have no choice as it does not make sense to pay for a service that I am not receiving. Whenever I travel, even to places which have only the most basic Xfinity internet speeds, everything works fine so the problem is clearly with Xfinity in my neighborhood.   I am at a loss.  Does anyone have any suggestions?