Apex domains cannot have CNAME records.
Question and response
Question
dig telefonica-ca.net. NS
Answer
telefonica-ca.net. 5 NS ns1.dominioabsoluto.com.
telefonica-ca.net. 5 NS ns2.dominioabsoluto.com.
Authority
The response has no authority records.
Additional
ns1.dominioabsoluto.com. 5 A 217.116.0.186
ns2.dominioabsoluto.com. 5 A 217.116.0.187
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0