Apex domains cannot have CNAME records.
Question and response
Question
dig teisa.com.py. NS
Answer
teisa.com.py. 5 NS ns2.teisa.com.py.
teisa.com.py. 5 NS ns3.teisa.com.py.
teisa.com.py. 5 NS ns1.teisa.com.py.
Authority
The response has no authority records.
Additional
ns1.teisa.com.py. 5 A 131.161.254.1
ns2.teisa.com.py. 5 A 131.161.254.2
ns3.teisa.com.py. 5 A 3.143.83.175
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0