Connection issues - HELP PLEASE!-

Hi, I just signed up for xfinity, I have my own SB6183 modem (which is in the list of equipments that work in xfinity page) with a Netgear WiFi router (also works), I'm plugging in the coax cable to the wall jack and the modem, and the RJ45 from the modem to the router, I'm not getting any signal to the modem, it's not receiving (modem and router are new by the way), I'm following the steps on xfitnity activation page but says something like "sorry, can't find this device" I'm thinking that it might me something with xfinity end? I have tried multiple times for literally hours to get in touch with technical support with no luck, I don't know what to do other that if I don't get help in the next days, I'll cancel and move on to another provider THAT HAS PEOPLE TO HELP and not dumb answering machines.