Need to recover information from a reformatted external drive
PhotoRec is a free program that I've used that may help you recover files. http://www.cgsecurity.org/wiki/PhotoRec

However, some information may not be recoverable no matter what you use, such as folder structures. Whatever you do, don't save any new files to the drive, and probably leave it off unless you are recovering. If you are uncomfortable, there are lots of places that will do data recovery for you.

You probably already know that you were unable to write to your external drive if it was formatted with NTFS.