Concrete column/structure behind drywall
Brick, poured concrete, concrete block are all likely possibilities in a 4-story building.
The solution generally would be the same on all of them: Hammer drill + an appropriate type of fastener. There are a number of different types. One popular one (at least in the US) is Tapcon:

though in this case, I would head over to my local hardware store to see the options first-hand and, if you can find someone there who knows what they are doing, get some advice.
I would consider cutting out a small square of drywall around each fastener location so that you are drilling directly into the brick/concrete/block. Otherwise you may get quite a mess trying to drill through the drywall into the other surface.
Depending on the specifics, sometimes it makes sense to cut out a large section of drywall, attach a piece of wood using appropriate screws and then mount the TV to that wood with wood screws.