Apex domains cannot have CNAME records.
Question and response
Question
dig cust.tele2.se. NS
Answer
cust.tele2.se. 5 NS kista.dns.swip.net.
cust.tele2.se. 5 NS kalmar.dns.swip.net.
Authority
The response has no authority records.
Additional
kista.dns.swip.net. 5 A 192.71.220.9
kalmar.dns.swip.net. 5 A 192.71.180.46
kista.dns.swip.net. 5 AAAA 2a00:801:103:a:0:0:0:f00d
kalmar.dns.swip.net. 5 AAAA 2a00:801:103:f:0:0:0:beef
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0