3 unleashed Dogs attacked my dog on a leash

My mom called me crying saying she was walking our dog in the desert behind our house when 3 unleashed dogs ( one was a German Shepard) ran up to our dog and started to pin him down and attack him. She kicked one in the face and my dog proceeded to break his leash and try to run away. But he was chased down and they started to attack him near the throat again. My mother is disabled and in no way could have fended off these dogs. The owner came running by and didn't even say sorry to my mom but just started hitting and cussing at his dogs then walked away. What should we do? He seems fine and doesnt appear to be injured. Just covered in dirt and mud. I feel so sad for my boy