Apex domains cannot have CNAME records.
Question and response
Question
dig eisp.pl. NS
Answer
eisp.pl. 1 NS virgo.kasat.net.
eisp.pl. 1 NS ns1.eisp.pl.
eisp.pl. 1 NS ns1.je.st.
Authority
The response has no authority records.
Additional
ns1.je.st. 1 A 85.159.214.98
ns1.eisp.pl. 1 A 82.96.91.2
virgo.kasat.net. 1 A 82.96.114.101
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0