Apex domains cannot have CNAME records.
Question and response
Question
dig tele3.us. NS
Answer
tele3.us. 3 NS ns3.tele3.eu.
tele3.us. 3 NS ns2.tele3.cz.
tele3.us. 3 NS ns1.tele3.cz.
Authority
The response has no authority records.
Additional
ns1.tele3.cz. 3 A 81.0.217.111
ns2.tele3.cz. 3 A 95.80.251.222
ns3.tele3.eu. 3 A 88.99.217.250
ns1.tele3.cz. 3 AAAA 2001:1528:123:0:0:0:0:d01
ns2.tele3.cz. 3 AAAA 2001:4de8:fa71:7e1e:0:0:0:d02
ns3.tele3.eu. 3 AAAA 2a01:4f8:10a:42db:0:0:0:d03
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0