Apex domains cannot have CNAME records.
Question and response
Question
dig a2b-internet.com. NS
Answer
a2b-internet.com. 5 NS ns.ezisp.eu.
a2b-internet.com. 5 NS ns.ezisp.nl.
a2b-internet.com. 5 NS ns.ezisp.org.
Authority
The response has no authority records.
Additional
ns.ezisp.eu. 5 A 91.213.13.111
ns.ezisp.nl. 5 A 95.217.237.33
ns.ezisp.org. 5 A 91.213.13.222
ns.ezisp.eu. 5 AAAA 2001:67c:1064:91:0:0:0:111
ns.ezisp.org. 5 AAAA 2001:67c:1064:91:0:0:0:222
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0