Apex domains cannot have CNAME records.
Question and response
Question
dig premiumwebservers.com. NS
Answer
premiumwebservers.com. 5 NS ns2.premiumwebservers.com.
premiumwebservers.com. 5 NS ns.premiumwebservers.com.
Authority
The response has no authority records.
Additional
ns.premiumwebservers.com. 5 A 91.121.48.173
ns2.premiumwebservers.com. 5 A 91.121.56.221
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0