Apex domains cannot have CNAME records.
Question and response
Question
dig grupohost.net. NS
Answer
grupohost.net. 5 NS ns10.hostdominicano.com.
grupohost.net. 5 NS ns13.hostdominicano.com.
grupohost.net. 5 NS ns12.hostdominicano.com.
grupohost.net. 5 NS ns11.hostdominicano.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0