Cannot connect external extension using proper settings, Cisco/Linksys router and FiOS

I am experiencing an error where I cannot connect an external SIP phone to a FreePBX Distro server. The attempt to connect doesn’t even reach sip debug.

The server is behind a NAT with port forwarding properly applied (5000-5082 UDP & 10000-20000 UDP port forwarded to the internal IP).

I have also enabled SIP NAT in Advanced SIP Settings and configured the NAT internal and external IP settings. I have also enabled NAT in Advanced Settings under the SIP heading.

I currently have a Cisco/Linksys router using a static IP provided by Verizon FiOS.

Make sure SIP ALG (or whatever your particular router calls it) is not enabled if you configure External IP in FPBX. They will fight each other. Asterisk works well with FIOS.

I also disabled sip alg on both routers - the nat where the server is hosted and where the external extension is located. Could it be anything else?