Apex domains cannot have CNAME records.
Question and response
Question
dig ptr.kartelkomi.ru. NS
Answer
ptr.kartelkomi.ru. 5 NS ns4.kartelkomi.ru.
ptr.kartelkomi.ru. 5 NS ns3.kartelkomi.ru.
Authority
The response has no authority records.
Additional
. 0 OPT ; payload 1232, xrcode 0, version 0, flags 0