Apex domains cannot have CNAME records.
Question and response
Question
dig hostserv.eu. NS
Answer
hostserv.eu. 5 NS ns1.hostserv.eu.
hostserv.eu. 5 NS ns2.hostserv.eu.
hostserv.eu. 5 NS ns3.hostserv.eu.
Authority
The response has no authority records.
Additional
ns1.hostserv.eu. 5 A 82.220.34.231
ns2.hostserv.eu. 5 A 5.79.97.178
ns3.hostserv.eu. 5 A 94.130.74.45
ns1.hostserv.eu. 5 AAAA 2001:1680:101:1:0:0:0:2
ns2.hostserv.eu. 5 AAAA 2001:1af8:4700:a120:4:0:0:2
ns3.hostserv.eu. 5 AAAA 2a01:4f8:c0c:289d:0:0:0:2
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0