How to check files which are deleted but their occupied space is not released ?

Use lsof command to check the list of files used by currently running processes.

[root@MY-SERVER logs]# lsof

You can use filter of files using grep

[root@MY-SERVER logs]# lsof | grep logs

....

....

java   root   96ww   REG   6148 /opt/application/MYAPP/logs/my_tests.log.lck (deleted)

java   root   98w      REG   6150 /opt/application/MYAPP/logs/my_tests.log (deleted)

java   root  101ww  REG   6153 /opt/application/MYAPP/logs/jonas_wsdls.log.lck (deleted)

java   root  102w     REG   6154 /opt/application/MYAPP/logs/jonas_wsdls.log (deleted)

java   root  1w         REG   6145 /opt/application/MYAPP/logs/startup.log (deleted)

java   root  2w         REG   6145 /opt/application/MYAPP/logs/startup.log (deleted)

java   root  105ww  REG   6160 /opt/application/MYAPP/logs/startup-2015-10-06.3.log.lck (deleted)

java   root  106w     REG   6161 /opt/application/MYAPP/logs/startup-2015-10-06.3.log (deleted)

java   root  223w     REG   6171 /opt/application/MYAPP/logs/webservice.log (deleted)

su      root  cwd       DIR    3072 /opt/application/MYAPP/logs

grep  root  cwd        DIR   3072  /opt/application/MYAPP/logs

lsof   root  cwd        DIR   3072  /opt/application/MYAPP/logs