Apex domains cannot have CNAME records.
Question and response
Question
dig dtn.net.ua. NS
Answer
dtn.net.ua. 3 NS ns1.bestname.com.ua.
dtn.net.ua. 3 NS ns2.bestname.com.ua.
dtn.net.ua. 3 NS ns3.bestname.com.ua.
Authority
The response has no authority records.
Additional
ns1.bestname.com.ua. 5 A 194.28.173.2
ns2.bestname.com.ua. 5 A 135.181.208.108
ns3.bestname.com.ua. 5 A 5.9.177.93
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0