Not sure how undelete works, but you are better off using diskdigger, you can root and use this as when you delete something it is not removed from the storage, it just removes the link to the files location and says that the location can now be overwritten. This means that if it is not overwritten then the data is still there, this is what diskdigger uses.
This also means you don't want to write any more data to your phone than is necessary until you recover your files as this will increase the chance of corrupting them.
(Rooting is write heavy)
The way to recover without rooting is to mount your phone to your computer as an external storage device then run the desktop disk digger application targeted at the phone storage, this should recover the files.
Note: this will recover all the files that have traces left on the drive so be prepared to trawl through them all looking for what you want.
Hope this helps, post back if needed.
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