Apex domains cannot have CNAME records.
Question and response
Question
dig MTSNET.RU. NS
Answer
mtsnet.ru. 4 NS ns4.mts-ws.net.
mtsnet.ru. 4 NS ns1.mts-ws.net.
mtsnet.ru. 4 NS ns2.mts.RU.
mtsnet.ru. 4 NS ns3.mts.RU.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0