Apex domains cannot have CNAME records.
Question and response
Question
dig bb.vodafone.cz. NS
Answer
bb.vodafone.cz. 5 NS ns1.vodafone.cz.
bb.vodafone.cz. 5 NS ns2.vodafone.cz.
Authority
The response has no authority records.
Additional
ns1.vodafone.cz. 5 A 217.77.165.80
ns2.vodafone.cz. 5 A 217.77.161.130
ns1.vodafone.cz. 5 AAAA 2a00:11b0:5:1:0:0:0:80
ns2.vodafone.cz. 5 AAAA 2a00:11b0:5:0:0:0:0:130
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0