Someone logging with my name and locking the server

Hey there,

Well I'm into a very very bad situation where my server is regularly being hacked and locking it using admin lock command. He is joining with the RCON admin's username i.e Rohit (myself)
In the logs I can see he's entering wrong password and within some time he leaves and when i check the server its locked.

Here is the log of him joining and leaving :-

[16:08:34] [join] Rohit has joined the server (0:77.234.146.48)
[16:08:46] LOGIN: Failed Login: Rohit. Wrong password (fhd) (1)
[16:10:20] [part] Rohit has left the server (0:1)

Also no other failed login attempts, so I assume he must have logged in with a wrong password.

Please help!