Apex domains cannot have CNAME records.
Question and response
Question
dig i02-5.onvol.net. NS
Answer
i02-5.onvol.net. 5 NS ns.melitacable.com.
i02-5.onvol.net. 5 NS ns1.melitacable.com.
i02-5.onvol.net. 5 NS ns2.melitacable.com.
Authority
The response has no authority records.
Additional
ns.melitacable.com. 5 A 212.56.128.132
ns1.melitacable.com. 5 A 212.56.128.196
ns2.melitacable.com. 5 A 34.159.187.214
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0