Apex domains cannot have CNAME records.
Question and response
Question
dig gigainternet.pl. NS
Answer
gigainternet.pl. 5 NS ns2.gigainternet.pl.
gigainternet.pl. 5 NS dns1.gigainternet.pl.
gigainternet.pl. 5 NS dns2.gigainternet.pl.
Authority
The response has no authority records.
Additional
dns1.gigainternet.pl. 5 A 91.123.176.2
dns2.gigainternet.pl. 5 A 91.123.191.2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0