Apex domains cannot have CNAME records.
Question and response
Question
dig supertel.dk. NS
Answer
supertel.dk. 5 NS ns3.v2tel.dk.
supertel.dk. 5 NS ns2.v2tel.dk.
supertel.dk. 5 NS ns1.v2tel.dk.
Authority
The response has no authority records.
Additional
ns1.v2tel.dk. 5 A 212.98.65.14
ns2.v2tel.dk. 5 A 212.98.67.14
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0