pbx.activecom.net has no CNAME records.
Question and response
Question
dig pbx.activecom.net. NS
Answer
The response has no answer records.
Authority
activecom.net. 694 SOA isaac.ns.cloudflare.com. dns.cloudflare.com. 2397206292 10000 2400 604800 1800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0