Apex domains cannot have CNAME records.
Question and response
Question
dig gemtel.com.mx. NS
Answer
gemtel.com.mx. 5 NS ns2.gemtel.com.mx.
gemtel.com.mx. 5 NS ns1.gemtel.com.mx.
Authority
The response has no authority records.
Additional
ns1.gemtel.com.mx. 5 A 201.130.4.162
ns2.gemtel.com.mx. 5 A 201.130.4.163
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0