I deleted the file from the itorrent app and selected Yes, and remove data but it's it didn't free up space. The storage is now getting assigned to other App's folders in iPhone storage section but it's not in there.  For example in this screenshot LocalSend is using 6.38Gb storage and file I deleted was about 6.32Gb. Is there any way to permanently delete the file from system. I've come across this problem before in android but file management is easier in android so I got to delete it from the file manager but I don't know how to do it on iOS .
Sorry, but I do not quite understand how storage occupied by iTorrent after deleting files could got occupied by other apps, and I also not sure what I can do here, iTorrent has ZERO access to storages of other apps, and "delete files" literally calls file system's file deletion functionality, you can check iTorrent's folder in Files app if it still has any files there
Even if you are correct and that's what happened, it would be iOS's bug it self, not iTorrent's
But if we remove the files from the Settings > iPhone Storage> iTorrent section, the space will be freed. While removing files from the Files app, iTorrent's Documents & Data still occupied space. @XITRIX