VOIP phone "Your call could not be completed as dialed."

We're moving our old landline to Xfinity VOIP;  after 1 hour with tech support we finally got a dial tone and were able to phone out OK.   People we called see our proper phone number, however despite 2 more hours with tech, everyone who phones us gets the "Your call could not be completed as dialed." message. 

 All we can get from tech support is to request a tech come to the house - and that could accomplish nothing, as it's clear it has nothing to do with our hardware - the problem is that Comcast didn't register our phone properly.

 Just whom at Xfinity can actually put our phone number into the proper database so other people can phone our number?