Dual trunk on Dual Nic with one ISP connection

We currently have a system with dual nics running a SIP trunk connection (main NIC) through an SBC supplied by our provider (no internet connection) and the second nic connected to our internal network and the SIP phones. The second NIC connection also provides the internet connection for the PBX for updates etc. So far so good!

We are adding another SIP trunk connection from another provider that uses regular internet service for connection. We have the trunk configured and it has registered and the provider has confirmed the registration, but no calls incoming or outgoing are working.

So a couple of factors here and i am unsure which or a combination of which are causing issues. We had this second trunk setup previously as a test and it worked great. Since then we have replaced the router and had not tested the trunk. We also went through a significant troubleshooting process with the primary provider during which a lot of the NAT settings on the PBX were changed. So currently the NAT settings under Asterisk SIP Settings are “never” and “Static IP” with the IP address of the NIC with the SBC connection.

So my thought is the NAT configuration is putting the IP of the SBC connection into the SIP header but i dont want to disrupt the primary connection. Could there be anything else that would be disrupting the secondary trunk? I have tried DMZing the internal address on the router and the SIP ALG is disabled. I have seen that the NAT is transforming port 5060 to another port but given that the registration is going through i am not convinced that this is holding up both incoming and outgoing calls.

Any suggestions?

Anyone have any suggestions?