Fritzbox and PfSense

[charneval]

Hello everyone,
I configured pfSense on a small network and everything works perfectly.
But I have a little 'problems in the correct operation of a VoIP PBX which puts it out the firewall receives calls perfectly but behind the firewall can only forward calls.
Unfortunately I haven't a third network card to do the DMZ, so I made a nat rule for port 5060 tcp / udp redirect to the internal IP PBX.
Think you can solve the problem but instead I still can not receive calls from outside.
Can you give me some advice or tell me if I have to do other configurations?

thanks
Andrea