Apex domains cannot have CNAME records.
Question and response
Question
dig cust.bredband2.com. NS
Answer
cust.bredband2.com. 5 NS pdns03.port53.se.
cust.bredband2.com. 5 NS pdns02.port53.se.
cust.bredband2.com. 5 NS pdns01.port53.se.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0