I got home yesterday to find that half of my hedge has been cut 
For context, the garden has needed a tremendous amount of work here. I do not proclaim to be a super gardener, but the hedge has improved a lot since we've been here with the right pruning - I am always out in the garden. This year, I have been letting the top of it grow up to even out the height ready for cutting in the autumn. To get home and find (half) of the top of it has been cut right back, and wonky, has made me quite cross.
Neighbour on the opposite side has no idea what's happened, neighbour on the side with the hedge is (so far) ignoring my text.
So as not to drip feed, the hedge is entirely on my land, it is not 'on the boundary' and therefore on my neighbour's land. The half that has been cut actually protrudes into my garden as it grew wonky, meaning my neighbour has some of my front garden. Prizes for guessing how long it's going to stay like that now!
Providing it is the neighbour, how do I be firm but fair in discussing this with them? I want to make it very clear that they are not to do anything on my property ever, but I don't want to fall out. This neighbour has told me that they felt out with the people who lived in our house before us. I think the friendship is definitely dented now though 