Apex domains cannot have CNAME records.
Question and response
Question
dig beltelecom.by. NS
Answer
beltelecom.by. 1 NS dns.belpak.by.
beltelecom.by. 1 NS nsrv.belpak.by.
Authority
The response has no authority records.
Additional
dns.belpak.by. 1 A 86.57.169.35
nsrv.belpak.by. 1 A 86.57.169.34
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0