S 33 won't regrister with Xfinity

Tried to activate an Arris S 33 with Xfinity, Xfinity said that my old 6190 modem is too slow for my internet speed, and I needed to upgrade.  My modem won’t activate, I have tried many times using the app, the light flashes green, and after 11 minutes the app says it couldn’t find the modem.  I hooked up a computer to the modem and on the status page is says security failed, and Docsis network access enabled, Status Denied.  Today, Xfinity came out to check my lines, I had a weak signal, they replaced lines and connectors and when the tech was done, I had a great connection.  He tried many times to activate the modem and couldn’t.  He finally called his tech people.  The tech lady tried to activate the modem on her side and said that it showed active, but wasn’t connected.  She said that she couldn’t see an IP address for this modem, and because of that, couldn’t activate the modem.  She told me to contact Arris and see if anyone has had this problem and how to fix this problem.  This modem is under warranty.  Hopefully someone can help me fix this problem and get my new modem to work like it should.