Apex domains cannot have CNAME records.
Question and response
Question
dig contactel.net. NS
Answer
contactel.net. 5 NS ns2.contactel.cz.
contactel.net. 5 NS ns.contactel.cz.
Authority
The response has no authority records.
Additional
ns.contactel.cz. 5 A 193.85.1.116
ns2.contactel.cz. 5 A 193.85.2.116
ns.contactel.cz. 5 AAAA 2001:af0:2:a:0:0:0:53
ns2.contactel.cz. 5 AAAA 2001:af0:2:b:0:0:0:53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0