Apex domains cannot have CNAME records.
Question and response
Question
dig pljtelecom.pl. NS
Answer
pljtelecom.pl. 5 NS ns1.plj.com.pl.
pljtelecom.pl. 5 NS ns2.plj.com.pl.
Authority
The response has no authority records.
Additional
ns1.plj.com.pl. 1 A 194.140.250.34
ns2.plj.com.pl. 1 A 80.72.32.6
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0