Apex domains cannot have CNAME records.
Question and response
Question
dig bestelclientes.com.mx. NS
Answer
bestelclientes.com.mx. 4 NS dns1.bestel.com.mx.
bestelclientes.com.mx. 4 NS dns2.bestel.com.mx.
Authority
The response has no authority records.
Additional
dns1.bestel.com.mx. 4 A 200.57.2.108
dns2.bestel.com.mx. 4 A 200.57.7.61
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0