Apex domains cannot have CNAME records.
Question and response
Question
dig mail-neoserv.si. NS
Answer
mail-neoserv.si. 5 NS ns2.avant.si.
mail-neoserv.si. 5 NS ns1.avant.si.
Authority
The response has no authority records.
Additional
ns1.avant.si. 5 A 152.89.233.30
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0