Apex domains cannot have CNAME records.
Question and response
Question
dig fxo.com.br. NS
Answer
fxo.com.br. 4 NS ns-550.awsdns-04.net.
fxo.com.br. 4 NS ns-1312.awsdns-36.org.
fxo.com.br. 4 NS ns-1680.awsdns-18.co.uk.
fxo.com.br. 4 NS ns-416.awsdns-52.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0