New modem, no dial tone

I installed a new Xfinity modem (model XB6-T) yesterday.  Internet connection works perfectly but after I returned the old modem to the Xfinity store I found I have no dial tone or voice connection.  If I call my phone number, it goes directly to voice mail.  I can access the voice mail on internet, but the phone never rings and I still have no dial tone.  The phone is plugged directly into the gateway, and the phone was working perfectly with the old modem.  I have re-installed the new modem--internet continues to work but still no dial tone.  I have followed all the suggestions on Xfinity help sites, but nothing works.  Xfinity apparently has no phone support, so I will have to drive in to their store to seek help in person.  I'm not very happy with this.