Ring group goest directly to no answer

We have a freepbx server in a datacenter that services different branches of a company spread throughout belgium. Each branch has its own custom context, trunk and ring group. The branches/Ring groups are:


When somebody calls the Antwerpen Ring group f.i. it jumps directly to the no answer option and Brussel is called.
The same happens with all other Ring groups. The weird thing is that when Brussel is called the same thing happens. The no answer option for Brussel is Brussel to and when i change this to f.i. Antwerpen ( so when Brussel doesn’t pickup Antwerpen is called) there is an endless loop.

Now for some background information:

The freepbx is installed on a server that has a public ip address so no nat is involved.

The telephones per branch are behind a nortel bsr252 modem/router that has Nat enabled and ports 5060(sip) and 10000-12000(rtp) are open. On the phones port 5060(sip) and 10000-12000(rtp) are set to be used. When i go to panel in the freepbx ui the extensions in the different ring groups are shown.

This is a mystery to me.

I appreciate any help.
Thank you in advance.