Trunk registering lan ip

don’t ask why but i have a vps with a openvpn server running all configured correctly i have a windows server and have tried 3cx to test and works fine and registers with vpn ip and can make and receive calls with good quality, now i want to use freepbx
i have set my external ip correctly which freepbx detected correctly anyway using the vpn.

i have nat enabled on trunk and in sip settings but on sipgate portal its registering with my lan ip for some reason and can receive calls.
i just cant work out why could anyone help me.

thanks