Apex domains cannot have CNAME records.
Question and response
Question
dig ktmtelekom.pl. NS
Answer
ktmtelekom.pl. 5 NS ns2.ktmtelekom.pl.
ktmtelekom.pl. 5 NS ns1.ktmtelekom.pl.
Authority
The response has no authority records.
Additional
ns1.ktmtelekom.pl. 5 A 93.159.189.243
ns2.ktmtelekom.pl. 5 A 51.254.196.157
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0