Neighbour throwing stuff onto our balcony

[Theonethingididntwant]

We live in a large block of flats and the people above us keep throwing all sorts out their window/off their balcony. At first I thought it was from loads of people above us but then recently I realised due to the way the balconies are staggered it can only be the flat above.
I was annoyed at the cigarette butts, the rubbish and random broken toys but didn't want to start anything as we didn't use the balcony in the winter.
Now the summer has arrived and our cats are out on the balcony a lot (supervised) as are we. It's not huge but it's starting to irritte me with all the disgusting stuff they throw down.
This weekend we were sat in the front room with the doors open due to the heat and a window that opens onto our balcony open too. We heard a noise like someone emptying water out and went out to realise they'd tipped some water or liquid out of their window and it hit our window... I was a bit . Wondering why on earth they didn't just pour it down their sink which (if it's the same flat as ours which all the flats seem to be) would be right in front of their window where it was poured out.
The next thing I know they've chucked some mushy food out and it's splattered on my balcony.
Then the water/liquid again but there was so much of it that it hit the window and came into our kitchen as well as covering the balcony.
I'm fed up with it. They also chuck KFC out the window to try and feed our cats. Obviously the cats now stand under their window meowing for their daily dose of fried goods.
I'm uncomfortable with confronting them because I know nothing about them. Im not sure what else I can do though and I can't see why anyone would use a window as a bin! It seems annoying and disgusting and I'm fed up with cleaning up after someone else's family on my balcony.
aibu to report them to the managers of the building? Or would it be better to not rock the boat?

Get on to the letting agency and ask if they can help. If they can't then you're going to have to woman up and talk to them. Don't be overly smiley, as I think they may not take you seriously. Be polite, but firm. It may be a child/teenager doing it and hopefully they'll be horrified.

If they continue to do it then collect everything in a lidded bucket and when it's nicely fermented, then put it back onto their balcony. 😁 Though, they're liable to put it back onto your balcony. I have spent the last few weeks collecting the chewing gum that the savage from next door is throwing onto my roof and garden. He can think of it as an investment as he'll be rewarded with a lump sum at a later stage. 😁

Put a net up? Even supervised your cats could come a cropper and it also deters birds etc in addition to bouncing off the KFC and shit thrown at it?

Also can you report then to the council? take a sneaky photo or video of it? they wont know that the report came from you, if they are throwing stuff at your balcony then they are likely doing this to others too.

Gross, report to lettings agent. They'll have to sort it.

Talk to them first, in case by some chance they are simply thick and don't realise (or it may conceivably be a child or an adult who lacks capacity).

If that gets nowhere, report and (I never say this) call police non-emergency number. We had a problem with someone chucking takeaway food all over our car regularly as revenge for asking the council to move a park bench used by local yoofs to drink late at night, and the police considered it vandalism and ultimately charges were brought.

I'd post anything I could pick up back through their letter box.

regardless of whether or not they know it's landing on someone else's balcony this is absolutely disgusting and i would report it to all and sundry