Apex domains cannot have CNAME records.
Question and response
Question
dig kei.pl. NS
Answer
kei.pl. 5 NS ns1.kei.pl.
kei.pl. 5 NS ns3.kei.pl.
kei.pl. 5 NS ns2.kei.pl.
kei.pl. 5 NS ns4.kei.pl.
Authority
The response has no authority records.
Additional
ns1.kei.pl. 5 A 94.152.254.100
ns2.kei.pl. 5 A 94.152.255.100
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0