Apex domains cannot have CNAME records.
Question and response
Question
dig ns7.ecomsiam.com. NS
Answer
ns7.ecomsiam.com. 5 NS ns7.ecomsiam.com.
ns7.ecomsiam.com. 5 NS ns8.ecomsiam.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0