Sorry if this is a long thread, bear with me! I’m a permanent council tenant who has recently moved into a new flat. Our communal garden is fenced off with 6 sheds facing our block which has 6 flats in it.
A tenant from another block, also fenced in on their side, is using my shed and has been using my shed for months maybe even years before I moved in. I called the council and someone from the neighbourhood team told me that they do not get involved in disputes regarding sheds and that basically it’s nothing to do with them.
They asked me are the sheds visible from where you are. I said yes and that I can see them from my window and that there are 6, presumably, for the 6 tenants that live in my block. The advisor then replied well then to me that sounds like 1 of the 6 is your shed. I advise you to put a note on the shed door stating that you’ve just moved in and that this is your shed and to give enough notice for them to move their items into their own shed. Which should be situated in their fenced off communal premises.
I followed the advisor’s advice and did this with the note on the shed, only to be met with confrontation and aggression. I did exactly what the council told me to do, to no avail.
What the other tenant did let slip is that he used to be very good friends with the previous tenant of my flat and that when they moved out, that they gave him the keys 
Surely, that is not allowed?
So my question is, AIBU to be upset by this and if so, does anyone have any advice as to how I should approach this matter?