Question about internet speed upgrade email

Yesterday afternoon I received an email from Comcast indicating that they are increasing my download speeds from 400 Mbps to up to 600 Mbps.  The email stated that this is included as part of my current plan and to take advantage of it all I needed to do was restart my modem.

My current plan as part of a quad bundle from Comcast is 105 Mbps.  I own my own modem-router combo, the Arris Surfboard SVG2482AC model which according to the information from Comcast will go up to 600 Mbps.  

I did restart my modem by disconnecting the electrical connection, leaving it sit totally off for about 20 minutes, plugged it back in and let it restart.  I then used a cabled connection from the back of the modem directly to my Surface laptop computer and used the speedtest.xfinity.com site to conduct a speed test and I am still getting just the 105 Mbps that I originally was.  I also tried the WIFI connection route and still came up with the 105 Mbps that I have always had.

I tried to find a phone number to contact Xfinity about this and did not have any success finding a number to call.  I tried a number of phrases on asking a question to the chat agent and still couldn't get any information about this.

So I was wondering if anyone here knew what was up with this or if the email was some sort of blanket mailing that really doesn't apply to me?