Apex domains cannot have CNAME records.
Question and response
Question
dig oeiizk.waw.pl. NS
Answer
oeiizk.waw.pl. 5 NS dns.oeiizk.waw.pl.
oeiizk.waw.pl. 5 NS ns.dinst.pl.
Authority
The response has no authority records.
Additional
ns.dinst.pl. 5 A 178.19.105.67
dns.oeiizk.waw.pl. 5 A 148.81.108.3
dns.oeiizk.waw.pl. 5 A 212.244.131.3
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0