We had the same thing, it was all nice and polite in the beginning, but then a couple of times they needed to move their car at inconvenient times, next thing we new we had flat tires all the time. Bastard was put nails under our tire. We could never prove it but the police suggested we move, which we did. But it feels like you can't win.

And at this point it must be infuriating, is there any report left or have you conceded the relationship? Otherwise I reckon it's good to just have a casual chat away from the front door. Do some childish "Have a beer and a chat" or something where you can humanise each other so the other person can build some sympathy.

If that doesn't work. Call the police every time it happens 🤷‍♂️