I have tried to put a lot of force (using the whole wheel [mechanical advantage]).

I could put more... but the wrench starts to bend a bit. so does the wheel!

I was thinking of soaking it in something, i read somewhere that might work. But im not sure what i should soak it in.

Also im looking for a specific tool that would attach to this 17mm square nut thing (the freewheel key thing).

In the pics, you will see that the key sticks out very little...

(paid 11eu for this frekin key. and 5 eu for the lbs guy to take apart my hyperglide cassette)