Apex domains cannot have CNAME records.
Question and response
Question
dig TENSORTELECOM.RU. NS
Answer
TENSORTELECOM.RU. 5 NS hdns2.mts.RU.
TENSORTELECOM.RU. 5 NS hdns.mts.RU.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0