Apex domains cannot have CNAME records.
Question and response
Question
dig digsys.bg. NS
Answer
digsys.bg. 5 NS ns2.digsys.bg.
digsys.bg. 5 NS ns.digsys.bg.
Authority
The response has no authority records.
Additional
ns.digsys.bg. 5 A 192.92.129.2
ns2.digsys.bg. 5 A 193.68.3.195
ns.digsys.bg. 5 AAAA 2a02:6a80:0:0:192:92:129:2
ns2.digsys.bg. 5 AAAA 2a02:6a80:0:0:193:68:3:195
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0