Apex domains cannot have CNAME records.
Question and response
Question
dig cust.keyyo.net. NS
Answer
cust.keyyo.net. 5 NS ns3.keyyo.net.
cust.keyyo.net. 5 NS ns2.keyyo.net.
cust.keyyo.net. 5 NS ns1.phonesystems.net.
cust.keyyo.net. 5 NS ns4.phonesystems.net.
Authority
The response has no authority records.
Additional
ns1.phonesystems.net. 5 A 83.136.161.92
ns4.phonesystems.net. 5 A 83.136.164.92
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0