[XtinaxFan]

I suggest painting a pentagram or upside down cross on your driveway and playing a lot of norwegian black metal or good ol' fashioned Cannibal Corpse - loudly. Do it in the afternoon so they can't complain about the noise.
Seriously though - if you have a letter slot on your front door write in permanent marker on your mailbox "post mail through front door please" to stop it being tampered with.
They sound like real bastards, if you are /can get friendly with people living next door to your neighbours ask if they are bothered by them too, if they are get them to complain to your landlord as well - adds more weight.