Apex domains cannot have CNAME records.
Question and response
Question
dig plesk.vispa.net. NS
Answer
plesk.vispa.net. 5 NS ns6.vispa.net.uk.
plesk.vispa.net. 5 NS ns7.vispa.net.uk.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0