100 mbps to 300mbps upgrade no improvement in download

Hello

I have upgraded the xfinity plan from 100 mbps to 300 mbps 2 days back. Done multiple resets with and with out customer care to get a signal refresh. By standing near very close to the Google router the speed I am getting is less than 100 mbps. Initially I thought it was modem issue. Mine was tp link 7610. Today I purchased a new mode netgear cm500 which has a max speed of 680 mbps. Router max speed is 1.2gbps.i am not even getting 50 percent of mentioned plan speed. What should I do next?