Dear Manish
At the time of posting to such cost center some messages must have been issued may be warning or information. Try changing the message into error message. It may be done through OBA5 probably. I am not in front of system otherwise could give you exact help. Else you can go to The path SPRO - Controlling - General Controlling - Change message control.
Secondly under control tab of CC you should put restrictions on actual as well as plan postings.
And also reduce the validity period of CC if you wish to restrict in that ways.
Regards
Rajneesh Saxena