I had a similer problem, but I knew who the culprit was, we had to move house twice to get away from them, I still get the occasional problem now, but nothing like it was, I was really ill because of it, lost loads of weight(put it back on tho) and nearly had a nervous break down, I would be targeted everyday as the kids were at the same school.
I felt like a criminal myself, as the police were always round my house, as what ever this person did to me, they would call the police and say I had done it to them. the police were absolutly s***
Why not go and seek advice from a solicitor, although if you have no idea who it is, it will be hard to do anything about it, can you not think of anyone at all who might be holding a grudge, the reason for it may seem really silly to you, but in their head its not.
People like this can be very very dangerous, as nafia said, my life was threatened on more than one occasion and my children were picked on and threated too, suffice to say I have one very angry 21 year old who has ended up with a binding over from the courts for trying to stick up for me.
Your best bet might be to move away if nothing can be done, I know this sounds like a drastic measure, but your sanity and peace of mind are worth it , believe me.:hug: :hug: