Not getting dial tone

I have not been getting a dial tone on my voice account for several weeks.  Every time I called Xfinity, I'm forced to reboot the modem.  Then I'm instructed I will get a call back to my mobile number after the reboot and it never happens.  I've rebooted my modem at least 5 times.  I have not been able to reach a live person directly.  Someone please help.