There isn't any way to restore the data, unless you have a previous backup. I am not a drive guru, but my understanding is that the drive is wiped.
I have read that when formatting new drives, it's best to remove a drive with data that you want to keep, so the scenario you describe does not occur.
As far as the disk sizes go, I don't understand why the capacity would have been reduced that much.
if you have access to a linux machine (you could use Knoppix), you could try mounting the drives directly to see if your files are on the drive. I doubt they are, but it might be worth a shot.