What DNS is authoritative for my domain
Solution 1:
You have to understand that DNS is a hierarchic system. This means that whatever DNS-servers the .ru-registry (a-f.dns.ripn.net) means are authoritative for your domain will also be the DNS-servers that will be asked when people try to resolve the domain.
Until the .ru-registry has updated the information regarding the domain to use your new name servers, your old name servers will be used.
Solution 2:
The domain registrar sets the authoritative name servers for the domain. The VPS will only become authoritative if you properly assign hostnames (such as ns1.MYDOMAIN.com & ns2.MYDOMAIN.com) and tell your registrar to use those as your authoritative name servers.