Calls not ringing

[kelvoshbogobog]

When making calls to mobile phones (just to mobile phones) the person making the calls does not hear a ringing, the line stays silent, then the person being called just picks up.
I've had a look through the logs but cannot see anything obvious.
Would anyone be able to point me in the right direction as to where to start looking please? I am pulling my hair out with this

Many thanks

 

[Evolute IT]

Trunk settings: Supports Reinvite and Supports Replaces. Both should be off unless absolutely required by your provider.

Try that; otherwise try a capture and see if 180 Ringing is received by 3CX.