Apex domains cannot have CNAME records.
Question and response
Question
dig pronet.bg. NS
Answer
pronet.bg. 5 NS ns125.superhosting.bg.
pronet.bg. 5 NS ns126.superhosting.bg.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0