That is absolutely aweful. I'm sorry it happened to you. Make sure to stay on top of that Rabies certificate -- if they can't produce it, you'll likely have to get a series of pretty painful shots.
(Been there myself, got attacked by a rottweiler back when my old dog was still a pup. The owner didn't stick around to provide any contact info after it happened.)
Della - GSD- DOB 10/23/13
Dina - GSD - RIP 09/01/98