Asterisk does not recognize event congested line

I have an unusual problem. I have configured two IP trunks configured on freePBX-2.8.1-17,asterisk-11.11.0-0,elastix 2.4. Everything works fine except that sometimes when the user makes an outgoing call, the PBX responds with music on hold. After some testing I found that the problem is related if the destination number is congested or have damaged the line. The phone provider sends a message when one of these events happens, but Elastix does not communicate this message, unlike sends music on hold.

This suggests to the user that Elastix has a problem, but in reality is just a congestion problem line or line damage.
How I can fix this? As Elastix can detect and notify the event correctly or to supply the error message supplied by the phone provider?

Elastix is not FreePBX. You would probably have better luck getting an answer from the Elastix forums.

This very well could have been a FreePBX bug. You are 4 releases and hundreds if not thousands of commits behind so before we can be sure FreePBX would need to be brought current. This is where it becomes a Elastix problem. They would have to support the transition to current builds. Doing this could very well break other things within their environment as they have an expectation of things being as they developed them. This is not unique to Elastix at all. Even in the FreePBX Disrto you need to do things the “distro way” for proper support. Once you go off the reservation and start changing things the system becomes quickly unsupportable.