Paying for Gb Internet service, but getting 3-500 wires and wireless.

I don't know what it is about Xfinity or my home, but I've had Xfinity I guess for going on probably close to a decade or something like that. Not one single year has gone by that something hasn't screwed up or stayed screwed up for years. I just don't understand how something can work so temporarily and then just be awful for most months out of the year. It's not like they can't flag this stuff on their own. They have the capability to look back and see, oh yeah, he's downloading at less than 75% of what he pays for. Of course, they don't do anything unless YOU are the one to complain and bring it up. I just want quality internet service.  I just went to bestbuy and purchased a S33 arris modem and switched out my other surfboard modem. no change whatsoever, in fact I think it's on average a little slower.