What @cynjut Dave is trying to say is create a new inbound route. Leave it as any/any and the destination should be set to simply terminate the call. Any did you have not created an inbound route then will hit this inbound rout and be hung up on.
Check if “hangup” actually disconnects the channel. Our SIP provider asked us to set it to “play sip tone” or “congestion” so they actually terminate the channel.