Netgear C6900 - Error message "Modem doesn't have built in Wifi"

I have a Netgear C6900 and I had checked before purchasing if this is compatible. I have been using it for a year now with no issues until today. I recently downloaded another Xfinity app so that I can see what other devices I have linked to my Wifi and saw there was a notification/error message. Error message reads "Your modem doesn't have built in wifi.  You can use this modem, but you won't be able to create a Wifi network without a separate router."  Has anyone else had this issue? I called Xfinity and they told me to call Netgear. I called Netgear, and the guy was rude and said they cannot help me and told me to call Xfinity.  I am now only seeing this error message when I downloaded one of Xfinity's other apps.  The normal My Account App does not have this.  Reason i found this was because I got notification from Xfinity that I used up 100% of my 1229 GB which is impossible. I have never even come close to this and I live alone.  All they kept telling me is that they will waive one month of the extra charge.  What I want to find out is what is causing this increase in usage.  I went and changed all my passwords for wifi just now in case someone else somehow gained access to my wifi.