Our solicitor friend emailed back last night and said that us writting the letter was the right thing. We did attempt to visit them twice.
We don't even know the names of the neighbours, they just know us as the owners of the block next door to them is all. Not like they are our friends.
We are not prepared to muck around with this, we just want them to hurry the hell up and get their crap off our property instead of treating it like it's their own. Their own yard looks like a rubbish tip and ours is starting to as well because of them!