Apex domains cannot have CNAME records.
Question and response
Question
dig insulardepuertas.com. NS
Answer
insulardepuertas.com. 5 NS ns1.insulardepuertas.com.
insulardepuertas.com. 5 NS ns2.insulardepuertas.com.
Authority
The response has no authority records.
Additional
ns1.insulardepuertas.com. 5 A 61.97.247.28
ns2.insulardepuertas.com. 5 A 61.97.247.58
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0