Apex domains cannot have CNAME records.
Question and response
Question
dig primevoip.it. NS
Answer
primevoip.it. 3 NS vins06.voiptelitalia.it.
primevoip.it. 3 NS vins05.voiptelitalia.it.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0