Apex domains cannot have CNAME records.
Question and response
Question
dig belbone.be. NS
Answer
belbone.be. 5 NS ns1.belbone.be.
belbone.be. 5 NS ns3.belbone.be.
belbone.be. 5 NS ns2.belbone.be.
Authority
The response has no authority records.
Additional
ns1.belbone.be. 5 A 213.181.52.200
ns2.belbone.be. 5 A 213.181.53.200
ns3.belbone.be. 5 A 213.181.54.200
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0