Under Siege

My Flat is the one on the right. Someone had completely destroyed my hedge while I had been at work! It can only have been the top flat again. A neighbour across the road watched them do it this morning not long after I had started work. The garden, in fact nothing on the ground floor level, belongs to them. Absolutely none of it. I noticed they had trimmed some of it off yesterday, which I didn't mind so much as that bit had been getting in the way a little and I had not had time to do it. But to totally trash that huge hedge which isn't even their garden in the first place I found absolutely shocking. I couldn't believe it when I got home. As soon as I saw what they had done, that was it. The hedge was the height of that branch sticking out they mysteriously left, with that width you can see at the bottom. It could take years for that hedge to reach its height again and months to go green again. It's almost bare. I'm afraid of what they are going to do next. Are they going to trash that large tree (on the right)? Change the locks? Do something to the back garden? What are they going to do? The nasty sods just left the mess they made on the front:

They just left the mess they made. It could not have been anyone else. The other troubles I have had with them in the past are:

My Bike being stolen from the Hallway a few months back. I had locked the door after I came in. Came out next morning to find it wasnt there. Only someone who had a key to the front door could have taken it. Either one of their friends or them. They would still know about it. The only other way out of the hall was through their flat. That bike cost me £100 as did its replacement.
I actually caught one of them attempting to steal and in fact mess with the seat on the bike before that when I left it in my own back garden. They then tried to say they got mixed up the bikes. Then they left their bikes in the hall. Some still do. About 3 live up there.
It may not be much but such things as helping themselves to my washing line without even asking. One of them left one of their bikes in my back garden a few months ago.
These people cannot be trusted. I haven't always been getting my bills, so have they been stealing the post too?
It doesn't help that these people are Afghans, I think. Their accents are hard to understand at times though one does speak good english. I know they have jobs. Don't know what they are.
Several times last year the police have been round looking for them. One was to do with a girl, the others were to do with immigration. I have always tried to be friendly and get on with them. All this behaviour by themselves is totally unprovoked.
It has got to stop. As far as I am concerned, all these incidents, including today, amounts to harassment. Legally and technically they have access to the front door and meters in the hall, their own flat and the fire exit - which they constantly use as a back door, coming in and out when they like - through the back garden which they have no legal need or access to, except for fire. Legally, going into my back garden, unless I say so, is trespassing.

From now on, I am going to keep a record of any incidents and take as many photos as I can regarding them. Rang my landlord and mate up Andy as soon as I got home and we are going to send them a letter by special delivery, backed up with my photos.