Apex domains cannot have CNAME records.
Question and response
Question
dig SMS-USLUGI.RU. NS
Answer
sms-uslugi.ru. 5 NS ns2.zcdn.ru.
sms-uslugi.ru. 5 NS ns1.zcdn.ru.
Authority
The response has no authority records.
Additional
ns1.zcdn.ru. 5 A 91.90.212.21
ns2.ZCDN.RU. 5 A 77.87.215.24
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0