I have just been in a very similar situation where i have had criminal damage done to my property, I reported it to the police, only to be told it was a civil matter, they will not sue because a judge would be likely to rule de minimus, in other words the cost of going to court would be greater than the cost of your fence,
They should by law disclose any bad relatioships with nieghbours at the time of the sale of the property, and if they havent already done so, I'm quite sure your new nieghbours would like to hear it from you, as they may have some claim against the people that sold the property to them, this may give you some satisfaction at a later date while you are errecting your new fence,
good luck.