ns4.register.bg has no CNAME records.
Question and response
Question
dig ns4.register.bg. NS
Answer
The response has no answer records.
Authority
register.bg. 4974 SOA ns.digsys.bg. hostmaster.digsys.bg. 2026030401 28800 3600 2419200 10800
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0