I rent a flat and have done for the last 5 years. It’s a block of 10 and I’m right in the middle. No issues, everyone gets on fine but my upstairs neighbours have been a nightmare on and off for the duration that I’ve lived here. Don’t get me wrong, we get on okay but it’s been hard sometimes. Anyway, I’ll get to my problem - it is an elderly couple who live above me with their son and 3 grandchildren. Grandchildren are all above age 11 (I think) but do suffer with some mental health problems/disabilities. For the last 5 years the kids have been sticking wet wipes/sanitary products down the toilet which have resulted in many blockages. The man hole is in my garden directly outside my living room and when it’s blocked the smell travels into my flat. I don’t even have to look to see if it’s blocked as I can always tell just by the smell 
Whenever this has happened I’ve called the water company and they have sorted it out. (If I don’t ring it doesn’t get sorted btw - apparently before I moved in the garden was overflowing as nobody had bothered to report it). The last couple of times it’s happened the drain (for the whole block) has been blocked and they’ve sorted it out fine and just sent out letters to remind everyone not to stick things like that down the toilet. I did ask them if they could send a letter specifically to my upstairs neighbour as we knew it was them causing the problem but they aren’t allowed to single people out. This time they’ve had a look and it’s just the drain that my upstairs neighbour and I use so it’s classed as a private issue. I’ve rang my landlady and she’s said she can’t afford to sort it out as she’s been out of work for the last year or so due to covid (not that I would expect her to pay for it anyway as I really don’t think it’s her fault). She’s contacted the neighbours to tell them to sort it out and they’ve said they will look into but not necessarily fix it. I’m just waiting to hear back. I’m hoping they won’t be awkward about it as they have been previously with other issues (their shower room was leaking into my bathroom last year and they denied it had anything to do with them at first until they were forced to sort it out).
What happens if they come back and say they can’t afford to fix it or just completely deny its them that’s caused the problem? Does the responsibility fall to my landlady? There is no proof that it’s them although it’s pretty obvious as there is 6 of them and only me in my flat. I don’t want to fall out with them but it’s a reoccurring issue and it’s really starting to piss me off as I’m the one that has to live with the smell and ring around to sort it out otherwise it just gets left. I feel incredibly sorry for the grandparents being left with a hefty bill but hopefully this will get the message across finally!!