Apex domains cannot have CNAME records.
Question and response
Question
dig zone.ee. NS
Answer
zone.ee. 4 NS ns3.zonedata.net.
zone.ee. 4 NS ns2.zone.ee.
zone.ee. 4 NS ns.zone.eu.
Authority
The response has no authority records.
Additional
ns.zone.eu. 4 A 217.146.66.65
ns2.zone.ee. 4 A 85.234.242.32
ns3.zonedata.net. 4 A 85.234.247.50
ns2.zone.ee. 4 AAAA 2a02:29e9:30:53:0:0:0:a
ns3.zonedata.net. 4 AAAA 2a02:29e9:20:53:0:0:0:a
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0