Apex domains cannot have CNAME records.
Question and response
Question
dig ip.cybergrota.com.pl. NS
Answer
ip.cybergrota.com.pl. 5 NS fns1.42.pl.
ip.cybergrota.com.pl. 5 NS fns2.42.pl.
ip.cybergrota.com.pl. 5 NS ns1.itservice4u.pl.
Authority
The response has no authority records.
Additional
fns1.42.pl. 5 A 79.98.145.34
fns2.42.pl. 5 A 51.38.99.90
fns2.42.pl. 5 AAAA 2001:41d0:701:1100:0:0:0:66c
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0