Android Question cant delete file

Hello,

I cant delete file from my application folder.

Android version is :4.4.2
Device: Samsung Galaxy Tab

There is permission "WRITE_EXTERNAL"

My app Folder : Haai
Sub Folder Name : Media

i tried

File.Delete (File.DirRootExternal & "/Haai/Media/",sFile )

and

File.Delete ("/mnt/sdcard/Haai/Media" ,sFile )

there is no error for both but file cant delete

any help