We had this problem several years ago.
I went to their house, when they were home, to try to talk to them about it.
They refused to answer the door.
I wrote a note, and taped it to their front door.
They sent a NASTY reply in the mail.
So, every time the dog barked like that, I called their home and had my son bark like a dog into their answering machine.
We had to do that about 5 times.
Then suddenly, the dog stopped barking.