Apex domains cannot have CNAME records.
Question and response
Question
dig customer.telia.com. NS
Answer
customer.telia.com. 5 NS dns2.telia.com.
customer.telia.com. 5 NS dns1.telia.com.
Authority
The response has no authority records.
Additional
dns1.telia.com. 5 A 81.228.11.67
dns2.telia.com. 5 A 81.228.10.67
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0