All screws can be unscrewed except for what can I do?
If it can be turned but does not come out, grab it with pliers and simply pull it out, then the thread in the housing is defective.
Screw is "screwed"
It can't be turned either
And I've already tried to open it with the pliers
Got the right bit? If the bit holder is "turned round" take a side cutter and turn it out with it. (Grab the head and press the side cutter firmly together)
I don't have a side cutter
Had to lend you one somewhere.
Is it possible without it?
You have already tried it with the pliers, drilling is also out of the question. Fear not otherwise.