Apex domains cannot have CNAME records.
Question and response
Question
dig hosting20.box3.pl. NS
Answer
hosting20.box3.pl. 5 NS ns2.box3.pl.
hosting20.box3.pl. 5 NS ns1.box3.pl.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0