Apex domains cannot have CNAME records.
Question and response
Question
dig cust.sover.net. NS
Answer
cust.sover.net. 5 NS clover.sover.net.
cust.sover.net. 5 NS dns2.firstlight.net.
cust.sover.net. 5 NS dns1.firstlight.net.
cust.sover.net. 5 NS maple.sover.net.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0