Apex domains cannot have CNAME records.
Question and response
Question
dig servidoresdns.net. NS
Answer
servidoresdns.net. 5 NS prometeo.servidoresdns.net.
servidoresdns.net. 5 NS atlante.servidoresdns.net.
servidoresdns.net. 5 NS menecio.servidoresdns.net.
Authority
The response has no authority records.
Additional
atlante.servidoresdns.net. 5 A 217.76.128.10
menecio.servidoresdns.net. 5 A 82.223.218.4
prometeo.servidoresdns.net. 5 A 82.223.191.10
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0