Apex domains cannot have CNAME records.
Question and response
Question
dig Korbank.PL. NS
Answer
korbank.pl. 4 NS dns.korbank.com.
korbank.pl. 4 NS dns.korbank.pl.
Authority
The response has no authority records.
Additional
dns.korbank.pl. 4 A 193.239.59.253
dns.korbank.com. 4 A 79.110.207.254
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0