Call the cops on her

What happened is unfair and it sucks, but still... it's great you called. It's always better to have tried to help an ungrateful idiot than to risk letting a poor woman die under the blows of her husband without doing anything. I'm sure a lot of abused women wish they had a neighbour like you.

No good deed goes unpunished I guess

There's a reason nothing was done, clearly.

And you then called the cops and filed an assault report, right?

Sounds like you interrupted some S&M play there. Apparently, she can take care of herself.

So call the cops on her assaulting you. She'll get away from the abuser ...

Isn't the whole point of calling "anonymously" to remain unknown? You're not supposed to have to talk directly to the police when you call anonymously. Specifically so that who ever you called on won't possibly see you talking to them and therefore, won't know who you are and possibly act aggressively towards you. Calling anonymously is supposed to prevent exactly what happened to you. It was a good thing you called, and it sucks that you got hit because you were trying to be helpful, but you should have given them all the information they needed over the phone, so you wouldn't have to talk to them in person and been able to remain...anonymous.

And now SHE can go to jail with her husband, since clearly they're both a menace to society.

If the girl complains about interfering in private matters, tell her it's no longer private if you can hear it through a wall.