Apex domains cannot have CNAME records.
Question and response
Question
dig isp.cotecal.com.ar. NS
Answer
isp.cotecal.com.ar. 5 NS ns1.cotecal.com.ar.
isp.cotecal.com.ar. 5 NS ns4.cotecal.com.ar.
isp.cotecal.com.ar. 5 NS ns3.cotecal.com.ar.
isp.cotecal.com.ar. 5 NS ns2.cotecal.com.ar.
Authority
The response has no authority records.
Additional
ns3.cotecal.com.ar. 4 A 200.50.248.11
ns4.cotecal.com.ar. 4 A 200.50.248.12
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0