Apex domains cannot have CNAME records.
Question and response
Question
dig trueinternet.co.th. NS
Answer
trueinternet.co.th. 5 NS conductor.asianet.co.th.
trueinternet.co.th. 5 NS piano.asianet.co.th.
trueinternet.co.th. 5 NS flute.trueinternet.co.th.
trueinternet.co.th. 5 NS clarinet.asianet.co.th.
Authority
The response has no authority records.
Additional
flute.trueinternet.co.th. 5 A 203.144.225.252
piano.asianet.co.th. 5 A 203.144.255.71
clarinet.asianet.co.th. 5 A 203.144.225.242
conductor.asianet.co.th. 5 A 203.144.255.72
flute.trueinternet.co.th. 5 AAAA 2001:fb0:100:0:0:0:225:252
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0