Apex domains cannot have CNAME records.
Question and response
Question
dig sinet.com.py. NS
Answer
sinet.com.py. 3 NS ns2.sinet.com.py.
sinet.com.py. 3 NS ns1.sinet.com.py.
Authority
The response has no authority records.
Additional
ns1.sinet.com.py. 3 A 138.99.100.5
ns2.sinet.com.py. 3 A 45.190.190.13
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0