Apex domains cannot have CNAME records.
Question and response
Question
dig fbnet.com.br. NS
Answer
fbnet.com.br. 5 NS ns2.fbnet.com.br.
fbnet.com.br. 5 NS ns1.fbnet.com.br.
Authority
The response has no authority records.
Additional
ns1.fbnet.com.br. 5 A 177.84.139.1
ns2.fbnet.com.br. 5 A 177.84.139.5
ns1.fbnet.com.br. 5 AAAA 2804:f04:0:2:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0