I would suggest establishing exactly what the problem is. If it is simply that you didn't consult them, then tough. You've apologised, there is nothing else you can do. If it's specifically the privacy issue, you may want to consider doing something about this. When you say "cedar slatted design" do you mean the thin horizontal, slightly spaced type? If so, it is true that they afford less privacy. Perhaps you should offer put up something on their side to obscure the gaps? I do think you neighbours are being completely unreasonable and the aggression is totally unacceptable. I would establish what their issue is, do what you reasonably can to rectify it and then be very, very clear, that their behaviour needs to be moderated. If it continues, report them to the council's anti-social behaviour unit, or get the police involved. Good luck, it sounds like a horrible situation to find yourself in and I hope you can resolve it soon.