I don't even know where to start with this.
Next door neighbour was a single man who lived alone and he died last year and his teenage (18) son moved in about 2 weeks later.
All was fine for a while but then one by one mates of his started staying longer and longer and now there are 5 teenagers living there.
From what I can gather 3 of them work at the same place (they all seem to wear the same uniform and share the same taxi but I have no idea where they work) and 2 of them stay at home all day every day.
So none of them really caused me any issues - yes its louder than usual because 5 blokes live there but during the week the noise stops around 11 ish which i am happy with.
I have had many discussions with the son who owns the house and he has been trying to make improvements to the house but there are many problems with it that his dad never got round to fixing such as the chimney breast his side is apparently very damp, the floor in the lounge is rotten, the windows in the kitchen are leaking and rotten (wooden frames), the bath is cracked and leaking, the boiler is broken, the attic is full to bursting with stuff, some roof tiles are missing.
Anyway, it is now apparent that the son has moved out leaving his mates living there because he couldn't cope with the amount of work that needed doing to the house.
Since the son has left the following has happened:-
Attic has been emptied and piled up out the back of the house
Front patio has been taken over with weeds
back patio has been taken over with weeds and dog mess all over it - the stench is lovely this time of year 
the garden has completely overgrown
the smell of weed coming from there is overpowering
Dog barking and waking me up at around 5am presumably as it needs to go out
the back door "sticks" so whenever they let the dog in and out the door has to be slammed repeatedly for it to shut
The rubbish bins when they do bother to put them out are just left on the pavement for weeks until one of the neighbours gets fed up of having to push the pram around it and puts it back in their front yard.
Girlfriends of the one guy has now moved in and they have loud sex and wake me up
I tried banging on the walls whenever any shouting/loud sex is going on but nothing changes, i have tried speaking to them but they never answer the door, when i do manage to bump into them when they are coming home I get apologies and promises to do things about weeds/garden/keeping noise down etc and nothing is ever done.
I have no way of contacting the son - they won't tell me where he is or give me a contact number
The land registry is still in his dads name.
I have phoned the council to complain about the rubbish and told them i can see rats running in and out of the rubbish but they are not interested in the slightest unless it was out the front of the house.
The other neighbours are disgusted by them also but as they aren't attached to them they are less bothered about it than I am - also at some point this year I am planning on selling my house but that's going to be impossible at his rate 
I had a council tax bill through the post yesterday but it wasn't my bill it was next doors i didn't realise until i had actually opened it. It's in the sons name with a single occupancy discount! There has been 5 people living there since last year so not exactly a recent oversight.
I'm half tempted to ring up the council and drop them in it but will they actually even do anything without proof?
What else can I do? If the state of disrepair continues surely its going to start affecting my house?