Apex domains cannot have CNAME records.
Question and response
Question
dig osinet.sg. NS
Answer
osinet.sg. 4 NS dns3.pacificinternet.com.
osinet.sg. 4 NS dns1.pacificinternet.com.
osinet.sg. 4 NS dns2.pacificinternet.com.
Authority
The response has no authority records.
Additional
dns1.pacificinternet.com. 4 A 182.23.148.37
dns2.pacificinternet.com. 4 A 45.117.188.93
dns3.pacificinternet.com. 4 A 210.24.236.53
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0