Apex domains cannot have CNAME records.
Question and response
Question
dig fiberdisk.com.ar. NS
Answer
fiberdisk.com.ar. 4 NS dns1.cvtci.com.ar.
fiberdisk.com.ar. 4 NS dns4.cvtci.com.ar.
fiberdisk.com.ar. 4 NS dns3.cvtci.com.ar.
fiberdisk.com.ar. 4 NS dns2.cvtci.com.ar.
Authority
The response has no authority records.
Additional
dns1.cvtci.com.ar. 4 A 24.232.0.17
dns2.cvtci.com.ar. 4 A 24.232.0.18
dns3.cvtci.com.ar. 4 A 181.9.215.6
dns4.cvtci.com.ar. 4 A 181.9.214.7
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0