If you encountered this situation, the most common cause for this to happen is a problematic setting within the Call Flow.
This means that you might need to redo the settings in your Call Flow, in order to receive incoming calls.
Access your Call Flow from your Admin Dashboard and Edit Call Flow for the User in need. Once you are in the flow builder make sure you don't just drag an Applet over, but look at each individual setting for that Applet. There are hundreds of combinations/possibilities to fit your business!