Apex domains cannot have CNAME records.
Question and response
Question
dig portotelecom.net.br. NS
Answer
portotelecom.net.br. 5 NS dns2.kinghost.com.br.
portotelecom.net.br. 5 NS dns1.kinghost.com.br.
Authority
The response has no authority records.
Additional
dns1.kinghost.com.br. 5 A 162.159.24.170
dns2.kinghost.com.br. 5 A 162.159.25.249
dns1.kinghost.com.br. 5 AAAA 2400:cb00:2049:1:0:0:a29f:18aa
dns2.kinghost.com.br. 5 AAAA 2400:cb00:2049:1:0:0:a29f:19f9
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0