Issue with calling certain numbers

Hello there,

Whenever we call [Edited: "Personal information"] or [Edited: "Personal information"] using one of our Comcast Business Voice SIP numbers we get the message from the carrier that “600 Busy Everywhere”.  I also get the same thing when calling [Edited: "Personal information"] or [Edited: "Personal information"].  I’m able to call my own cell number with no problems. I also called [Edited: "Personal information"] and [Edited: "Personal information"] with no problems. So I'm confused as to why those first two listed numbers don't work.

[Edited: "Personal information"]