Note that you must configure firewall to allow connections to port of CDR, by default it is not opened and you can't access 3CX server from another computer. This applies both for Windows and Debian.
Try using telnet in putty to receive CDR data from 3CX.
A trick -- you can use port 5015 for the purpose, configure it into CDR serrings, the reason is it remains open into firewall after 3CX installation.