ofertas.oi.com.br has no NS records.
NS records for this zone are defined at oi.com.br.
NS records for this zone are defined at oi.com.br.
Question and response
Question
dig oi.com.br.edgekey.net. NS
Answer
The response has no answer records.
Authority
edgekey.net. 180 SOA ns1-2.akamai.com. hostmaster.akamai.com. 1579440527 900 300 604800 180
Additional
. 0 OPT ; payload 4096, xrcode 0, version 0, flags 0