Apex domains cannot have CNAME records.
Question and response
Question
dig united-telecom.be. NS
Answer
united-telecom.be. 5 NS bonnie.ns.cloudflare.com.
united-telecom.be. 5 NS bayan.ns.cloudflare.com.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0