I had this happen to me when the game first came out (PS3).
Big Ant thought that maybe they could fix it, and I emailed them the save file. Unfortunately it was buggered (and overnight the corrupted file uploaded to my PS+ backup) so I had to restart.
Maybe they can help you?
Ever since then though - for any game I play - I back up not only to PS+ but also to a USB drive. In Dropbox I have about 30 game saves (PC and console) manually backed up just in case. It's a PITA but these things do happen, and if I'm that invested in a game I really don't want to have to lose all progress.
Backup, backup, backup.