Elastix 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?

This is not the place for supporting GUIs.

What message is being sent?

Have you configured music on hold instead of ring back tone? Otherwise, I would only expect music if there was an explicit indication that the line was on hold, from the remote end.

If they are sending you the message through a voice message , you should try using progress()…

This application will request that in-band progress information be provided to the calling channel. This is also known as “early audio” and “early B3” (for example: see Dial option /b in chan_capi-cm).