Close NavigationWindow (modal ) from another js file in Titanium IOS7

I am migrating a current project to 3.1.3 . I need a close button on the modal window so i had to use a NavigationWindow as suggested in the IOS7 migration guide. Here is what i have

btnSubscription.addEventListener('click', function(e) {
Ti.API.info('Subscription Button Clicked.');
openWindow("paymentsubscription.js", "Subscription");
});
 
function openWindow(url, title) {
var win = Ti.UI.createWindow({
    url : url,
    backgroundColor : 'white',
    modal : true,
    title : title
});
 
 
if (Titanium.Platform.osname !== "android") {
var winNav = Ti.UI.iOS.createNavigationWindow({
    modal: true,
    window: win
});
}
if (Titanium.Platform.osname !== "android") {
    winNav.open();
}
else {
    win.open();
}
}

Now on paymenttransaction.js i was previously doing this when i was using titanium 2.x

var mainWindow = Ti.UI.currentWindow;
 
var mainWinClose = Ti.UI.createButton({
style : Ti.UI.iPhone.SystemButtonStyle.DONE,
title : 'close'
});
 
if (Titanium.Platform.osname !== "android") {
    mainWinClose.addEventListener('click', function() {"use strict";
mainWindow.close();
});
responseWindow.setRightNavButton(responseWinRightNavButton);
mainWindow.setRightNavButton(mainWinClose);
}

The problem i am facing is that i need to close winNav in the case of IOS and not win anymore. In paymenttransaction.js i was previously using

var mainWindow = Ti.UI.currentWindow; But now i need to close the navigation window(winNav) and this does not hold good anymore. Is there anyway to do this? . Is there a Ti.UI.currentWindow equivalent for NavigationWindow ?