Apex domains cannot have CNAME records.
Question and response
Question
dig cable-sur.com.mx. NS
Answer
cable-sur.com.mx. 5 NS ns3.mysecurecloudhost.com.
cable-sur.com.mx. 5 NS ns4.mysecurecloudhost.com.
cable-sur.com.mx. 5 NS ns1.mysecurecloudhost.com.
cable-sur.com.mx. 5 NS ns2.mysecurecloudhost.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0