Forgive me this is going to be epic and humiliating so have name-changed but I need to unload and get it all out in one and it has probably been moaned about loads before.
Moved in here about 15months ago, big old building (so no soundproofing, wooden floors etc), mostly owner occupier and mostly quite elderly so quiet, look after each other and all happy to have a poorly dc to dote on. Travelled a lot last year so wasn't around every weekend and only noticed occasional gatherings upstairs that got a little loud drunk chatty but generally seemed to be not too intrusive or late. Very quiet over summer then a BIG party followed by lots of DIY type noise leading me to think new owners were in and hopefully all would quiet down after the initial housewarming, settling in and then realising that your neighbours can hear EVERYTHING!
Wrong. Every other weekend, friday night preclub party upstairs, first I know is flat filling up with people from 930pm doesn't stop til after 1am. Then back at 4am crashing about, slamming doors etc. This is on top of 4am noisy taxi deliveries to the front door on thur/sat/sun, (thurs is student night here) so 4 nights per week plus the occasional tues or wed thrown in for good measure. New Year's Eve was the tipping point when I was woken at 530am by someone coming back putting on music for half an hour then turning it off (by which point I was up with dc) then once the bells went and my other neighbours came over for a drink and left about 1am, we all went to bed and upstairs party started at 2am and went on until 530am. I was zombie mum on new year's day, and lots of saturdays after.
There was a leak in my ceiling one feb eve so I had opportunity to meet upstairs neighbour, show her my flat, point to teeny tiny dc wheelchair next to front door and heavily hint that we were being very quiet because dc is asleep. Hoped that would do it. Nope, but had contact details now from girl I met who told me she and her flatmates owned the flat, cut to the following weekend and I texted her at 1am to say my 3yo has now been up for 2 hrs so please turn off music thanks. No answer, music went off then back on quieter a little later, until after 3am. Got a message the next day apologising, she wasn't there and would ask flatmates to keep it down in future. I asked her to please come for coffee (so I can have a civil shut it type chat) and gave a couple of different times, no answer, contact stopped.
So next party I called 101, no one showed. Next party I called 101 and really insisted they come over. They did, twice, because party goers smoking outside saw them coming so when upstairs heard my door go they all went really quiet, then cheered once the noise team left (they had heard the party coming up the street anyway so went around the block and then logged it). When the noise team did go up and ask for the party to move on the students refused on account of they were going out in an hour anyway?!? They did go out an hour later (1am) but not before stamping repeatedly on the floor whilst yelling 'fuck you fuck you' all the way around the flat and into the street, really intimidating. And that was that, just advised to keep logging complaints.
The guy in the flat above theirs is the unofficial factor for the stair and called me about some repairs, whilst talking I find he is also bothered by the noise, though not quite as bad, and the rest of the neighbours in the stair are narked by the front door banging and stair noise etc.
Turns out it is a student flat upstairs from me and the flat is owned by the mother of the girl I met not the people living there, we all think maybe 4 or 5 people live there, which is more in one flat than all the other flats put together. There is no landlord listing or HMO license or anything, not familiar with the rules but it seems they consider themselves exempt. So I get the number for the owner but hesitate in calling because I figure it could go either way since I am calling a mother to complain about her child and I am not good at confrontation, hate it.
Following the noise team intervention the students up the ante by stamping, properly slamming their way about at all hours and frequently waking us all up. After a month of thinking I have no choice but to call owner I realise the plaster on my ceilings is cracked, in every single room and so I make the call.
Spoke to father first, who was mortified, then was called back by mother who was very apologetic, this year's lot of students are a lot younger than last year's phd students; any more parties and they are out etc etc. All good, and she is visitng the following week so will come and see the damage. And the only people who live there are her daughter and two others!
Between that conversation and the next, the tone completely changed and I was hearing noise from another flat perhaps, or they were good students who never went out drinking, I must be thinking of someone else 
!?! Oh and the party the team were called too was just a little dinner party with one or two guests. The factor guy also tried to have a chat with her and got the same line, total denial. Her answer to my cracked ceilings? Oh well I have seen worse !!!
Anyhoo all was good for a couple of weeks after her visit (which was to oversee floor sandings, she refused to consider carpeting, and also swapping a same size bedroom with a sitting room so that their sitting room is not above a bedroom because their bedroom is carpeted so no compromise whatsoever). I was told to contact owner directly and not council noise team in future.
Then last weekend we had a return to evening stampathons resulting in me texting owner at 10pm sun eve to ask that the students please stop banging around because dc was ill from 4th disturbed night in a row. The phone went upstairs immediately and then all quietened down so I went to sleep and was woken later by her ringing me at almost 1am to say she had just received my text and had spoken to the students and woken them up so ~I must be sensitive to noise and hearing it from another flat 
! There were no more visitors or music or anything that could be causing a problem and obviously the students were just walking around and being as quiet as they could, blah blah blah. This went on for a bit with her totally trying to gaslight me into thinking I have a crazy imagination, lucky I was tired or the conversation would have ended very abruptly, as it was I just said mhhmm a lot and got off as soon as I could. She did relent and give me their landline to call them if they are being noisy.
Now this evening guests arrived upstairs at 1130pm, waking dc, and left about 1am when I started banging about flushing loo etc really noisily to make them realise we are awake and fuck the actual fuck off which they did eventually in staged groups, thinking they were being sneaky but the drunk high heels on wooden floors and hysterical laughter outside the front door as they scarpered kind of gives the game away, no 
?
I considered calling them but figure there is no point, they have no intention of stopping this and anytime I try to communicate the situation just gets worse and I can't be bothered with being woken up repeatedly whilst they try to get even or whatever it is they are doing.
I will move 
, (I rent and the flat and other neighbours are lovely), but it won't be immediate and I need a short term solution. I am sure owner told me initially they were finished in june and there would be a new tenant but when I last spoke to her that seemed to change to september and I really don't think she can expect us all to put up with this crap until then, also I fucking object to being called a liar, (as does neighbour two up) because owner has to believe what students say and can't we see that ( no I fucking can't they are overgrown nocturnal teenagers with no morals), AIBU?
And congrats if you made it this far 
, I feel a bit better now I wrote it all down!