Just to recap first - you changed the port in 3CX "General Settings" tab to 5062 and updated the configuration of the softphone to the same, and you said you are connecting over NAT - so softphone is not on same LAN?
If it is not I would suggest starting with a softphone on the same LAN, and make sure that it connects. This would help to establish if problem is with 3CX <-> Softphone setup, or elsewhere (port forwarding to 3CX from WAN, port blocking at softphone location, etc.).
Gotta start somewhere and basics always best place to start.