You could go the opposite way. Advertise for them everywhere. Put up signs for cheap stuff in other turfs. Let the free market work.
Now is the problem the people below or where you live? Getting rid of thek might bring someone worse. Sounds like you have grown out of the area.
For example, had issue few years back for noise, they came out attacked me, then called police and made out I attacked them. They have also made many false reports to the polcie and they quickly come out to them. Yet if I report them, even case of when they had guns and kelos in the place - they ignored me and only came out when I said I'd kill myself if they don't do anything, too which they still did nothing about them and even talking to the officers, they were aware of what they are like and yet stil did nothing and all i got was platitude. It really is most shocking.
I said I would setup a recording system that would record their activities and I one of the officers said we would love that, yet even after doing that with many recordings, none of them care and I've even played recordings to police and what did they do. Yes, told the local officers who in turn told the dealers and you can guess how that worked out.
I even have email proof of officer admitting they `accidently` put a note thru their door with my details, I kid you not and what did they do - well they said sorry and if I had a penny for every sorry I've had over the years, I'd be very rich.
It really is beyond belief and the police today in the UK and frankly not police but social workers who care more about being seen to do their job over it and any good officers been driven out the force and that's not just my opinion, it's a large proportion of many ex officers.
Look at the replies from ex-officer in this tweet: https://twitter.com/metpoliceuk/status/1243493123155689472
it's just not even the icing on the cake.
Sorry I need to step away form this now for my own health and will be back later once I stop shaking.
Calling the cops and telling them they have guns and kilos won't help because how would you know (in their minds) and why would they believe someone about ownership (they start looking at you). Any offers to setup your own operation makes it seem like you have something against the couple. Now you are the suspect.
Never threaten to kill yourself to get the cops attention because it will be focused on you not on why you are threatening to kill yourself.
Why do you continue to live there for years?
I threatened as it was true and I'm that desperate and I know that if I do that at least there would be some form of inquiry and sadly, that seems to be my best hope having tried all the right things.
I have many solutions that are wrong things and illegal that I could do to solve this, but again, against my morals. I'm happy to grey the law, but not break the law.
I've tried social engineering with some success and brief respites but again, limits. I've no issue hacking any dealers phones and the like and have done in the past and passed on intel, but alas downstairs are still there.
Don't get me wrong, I've done things and had some success.
Was entire ground floor of the 6 flats all junkies, one I managed to re-educate, another I socially engineered away.
2 corrupt coppers removed.
4 Gangs removed
Numerous habitual junkies - removed from area.
2 gangs removed from area via blackmail.
Probably missing few.
But I've not been idle and had some positive results, albeit using craft tricks, so bit grey legally but morally just.
However the real issue does seem to be a police informer, did have some limited success last year, managed to socially engineer two gangs and with that, they ended up taking each other out and also saw the downstairs issue beaten up. That managed to give me a break but they always get back to the same old same and with that, the only way is to out them and the police handler for the shite they have caused.
But for closure - I need them and the police handler publicly outed in a way that they can't cover and with that, need publicity to deal with them and in a way that sends a message to the police so they don't do it again.
So yeah, messy, but need to end-game this for my own health and see it thru for closure and for my health overall.
Hence, best solution would be a reporter I can trust and is respectable to traction this. That simple.