Hi Harshad
I find this in my support of clients, a common issue with spreadsheets. Not sure whether you are using a Windows based system or Linux based, but the fix is the same. Start off first with making sure your base operating system is regionalized correctly for your country / language etc. Windows is more the culprit for doing this, and sets defaults for American English, but you could have it wrong for your Linux as well.
If you correct it within the country/language settings (Windows - Control panel - Region and language)(Ubuntu Linux and other similiar distros - System Settings - Language Support - Languages)||, then your spreadsheet (and all other data for that matter) will tend to default to your global settings. You will see a section where you can correct the default date format. My country and language settings is the same as yours, date then month then year,and I have to correct mine this way as well.
Try this, I am sure you will resolve your mentioned problem.
Regards
Andrew Brown