Apex domains cannot have CNAME records.
Question and response
Question
dig provedormixnet.net.br. NS
Answer
provedormixnet.net.br. 5 NS ns1.udns.com.br.
provedormixnet.net.br. 5 NS ns6.udns.com.br.
provedormixnet.net.br. 5 NS ns3.udns.com.br.
provedormixnet.net.br. 5 NS ns4.udns.com.br.
provedormixnet.net.br. 5 NS ns5.udns.com.br.
provedormixnet.net.br. 5 NS ns2.udns.com.br.
Authority
The response has no authority records.
Additional
ns1.udns.com.br. 1 A 138.97.64.93
ns2.udns.com.br. 1 A 170.247.40.66
ns3.udns.com.br. 1 A 187.95.160.227
ns4.udns.com.br. 1 A 138.255.156.30
ns5.udns.com.br. 1 A 138.97.64.94
ns1.udns.com.br. 1 AAAA 2804:231c:beba:c0ca:0:0:0:93
ns2.udns.com.br. 1 AAAA 2804:231c:e500:cafe:0:0:0:66
ns3.udns.com.br. 1 AAAA 2804:a4:ffff:1600:0:0:0:227
ns5.udns.com.br. 1 AAAA 2804:231c:beba:c0ca:0:0:0:94
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0