I'm not surprised you're angry and upset. I would be too. I'd also be afraid for my dog's safety.
Given such a strong emotional response on behalf of the neighbour, I'd be wanting an explanation, I think. Why does he feel so strongly towards your dog? Do you let the dog in the garden and leave him to bark excessively, for example? Does the neighbour have cats/chickens/rabbits etc? If so, does your dog chase them/worry them? If you don't know why, it could be a case of mistaken identity, but you'll only know that if you speak to your neighbour.
I'm not victim blaming here, so I'm sorry if it comes across that I am, but if you know why your neighbour feels so strongly against your dog, then you can take remedial action.