Apex domains cannot have CNAME records.
Question and response
Question
dig biuro.internetia.pl. NS
Answer
biuro.internetia.pl. 5 NS ns2.internetia.pl.
biuro.internetia.pl. 5 NS ns3.internetia.pl.
biuro.internetia.pl. 5 NS ns1.internetia.pl.
Authority
The response has no authority records.
Additional
ns1.internetia.pl. 4 A 195.114.173.153
ns2.internetia.pl. 4 A 87.204.28.18
ns3.internetia.pl. 4 A 87.204.30.249
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0