Apex domains cannot have CNAME records.
Question and response
Question
dig topnet.com.mx. NS
Answer
topnet.com.mx. 4 NS ns1.strends.com.mx.
topnet.com.mx. 4 NS ns2.strends.com.mx.
topnet.com.mx. 4 NS ns3.strends.com.mx.
Authority
The response has no authority records.
Additional
ns1.strends.com.mx. 4 A 200.76.111.250
ns2.strends.com.mx. 4 A 200.52.138.68
ns3.strends.com.mx. 4 A 200.76.111.251
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0