It looks very much like a case of corrupted save...
If your game was on PC, I could suggest you number of ways to try dealing with the situation, and certainly a
way to prevent losing all progress due to save corruption in the future...
But with consoles unfortunately there is no cure, as far as I understand, but I'm far from being expert in anything regarding consoles, for example may be there are some ways to get inside the system that I don't aware of...
The huge disadvantage of one-save-slot system is that if your only save becomes corrupted, the only way to continue playing is starting entirely new game and ALL your progress is lost, simply because you don't have any older saves you can roll back to...But again, even when you start all over you have no guarantee the same thing will not happen in a middle of your new game...
With PC there is a theoretical way the developer could try to restore your current progress - by analyzing and fixing your save file which you can simply copy and send to him (although I never heard they did it for even 1 PC user). I have no idea how it could be done with a console, but again, if there was a way I don't believe they would do it for anyone...
So the bottom line, I'm sorry, but you're screwed...