Apex domains cannot have CNAME records.
Question and response
Question
dig vivozap.com.br. NS
Answer
vivozap.com.br. 5 NS comprido.vivo.com.br.
vivozap.com.br. 5 NS tiete2.vivo.com.br.
vivozap.com.br. 5 NS guandu.vivo.com.br.
vivozap.com.br. 5 NS pinheiros2.vivo.com.br.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0