If I had your problem, I'd try the following:
1/ open the car door with the physical key (pop the cap over the doorlock etc.) look in user manual or youtube if needed
2/ pop the hood of the car
3/ put a 12 volt battery charger onto the "jumper posts" and recharge the 12 volt battery. Again see the manual or youtube for locations
Hopefully that gives you access again
Good luck (hope I didn't misunderstand the problem)
I think I am having the same problem. I left the Volt for about a month and now it is locked. I called AAA and we put their charger on the 12 V battery in the trunk. Things started working again and we decided to leave it overnight on the two amp charge. I suspect things will look better in the morning. Not entirely sure why the 12 V ran down except that I was carrying the key fob around in my pocket and it was on from time to time. Probably operator error!