Apex domains cannot have CNAME records.
Question and response
Question
dig interplus.com.pl. NS
Answer
interplus.com.pl. 5 NS dns1.itservice4u.pl.
interplus.com.pl. 5 NS dns2.itservice4u.pl.
Authority
The response has no authority records.
Additional
dns1.itservice4u.pl. 4 A 145.239.89.74
dns2.itservice4u.pl. 4 A 217.182.74.65
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0