Hi,
I'm afraid the problem is another type -- Microsoft Lync (wtat is your other system) is using TCP for RTP media, i.e. for voice, while 3CX and almost all other PBXs, including Avaya, are using UDP for media. This could be the reason for not receiving any media.
Research this possible issue or raise a ticket to 3CX support.
Kind regards,
Orlin