Can I redo or extend a giveaway ?

Create a support ticket explain the situation. Since it was SG that was down so I think they will help you out.

According to this, you don't have any active giveaway... only one that has finished.

I don't know if there is a specific rule for this case but i assume that if the giveaway has finished then give the game to the winner.
If the giveaway didn't finish, you can delete it (But the delete will be recorded in your profile) and recreate the giveaway.

Create a support ticket. Your giveaway finished. Although most likely you will be told to give the game away to the winner of your giveaway, since there were multiple entries and all that.

Okay, thanks, I will try the ticket thingy

usually when site was down all GA gets automatic extension equal to lost downtime but not sure about yours