I have tried every combination, and it is either inverted or always on or
always off.


If you are not sure get someone who is to look at it, but:

With the mains isolated, first check the colours in the wall switch.
You should have a red and black here, but two reds are possible.

You should be able to see the separate cables entering the rose.
It is usual for one to be the supply, one to be the switch, and *in most
cases* one to feed the next fitting.

The supply and onward feed are joined red-to-red and black-to-black !PLUS!
the uninsulated or green/yellow sleeved earth cores are joined, along with
the earth to the switch. If there is no earth core, then you wiring is
out-dated and you should consider it's replacement.

The feed into the switch is connected to the red supply/feed pair, the
output from the switch (usually black often sleeved with red tape) will
connect to the brown/live of the pendant, the blue/neutral of the pendant
will connect to the black supply/feed pair.

Toby.