Apex domains cannot have CNAME records.
Question and response
Question
dig emfibra.net.br. NS
Answer
emfibra.net.br. 3 NS ns915.hostgator.com.br.
emfibra.net.br. 3 NS ns914.hostgator.com.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0