Apex domains cannot have CNAME records.
Question and response
Question
dig topsaas.net. NS
Answer
topsaas.net. 5 NS pdns.binat.net.il.
topsaas.net. 5 NS sdns.binat.net.il.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0