Apex domains cannot have CNAME records.
Question and response
Question
dig oxem21.net. NS
Answer
oxem21.net. 5 NS ns.oxem21.net.
oxem21.net. 5 NS nssec.online.net.
Authority
The response has no authority records.
Additional
ns.oxem21.net. 5 A 212.83.188.73
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0