Gigabit speed Issues

So going on over a month now I've been gettings slow speeds after work was performed in my Area. Before the issue I was getting 850mb-925mb Hardwire and Wireless 5Ghz 675mb-750mb. My house is setup with Cat6 and the New XB7 Comcast Modem. After there work in the area im now getting about 350-500mb hardwire and its not stable and Wireless is 250mb-475mb is also all over. I have also noticed on somedays it will spike to 650MB but then throttles down to 250. Please fix and explain this. Also when I connected to a Private VPN i get alittle better speed which tell me comcast is either throttling my connection or a comcast line/node issue Please fix ASAP.

Im paying for Gigabet speeds please fix