Sip Nat config Zoiper?

[killmasta93]

Hi,

I was wondering if someone could shed some light on the issue im having. Currently having working perfectly asterisk with my Trunk Sip VOIP provider (UNE based on colombia south America) Currently trying to use zoiper using SIP for the users to call the office, the issue is that they cant hear each other. after hours of researching found out in the sip.nat config i would put this

nat=yes
externip=mywanip
externhost=mywanip
localnet=192.168.1.0/255.255.255.0

after reloaded it starts to working the zoiper calls both sides can hear BUT after few mins users started to say that the calls weren't coming in to the Trunk Sip of my VOIP provider so i had to remove those lines on the sip nat config any idea how to troubleshoot this i know its a nat thing but dont know where to look.
Now my question is, did i miss something on the firewall? As i have the NAT 5060 and 10000-20000 opened

Thank you