@mismi,
It has got to be the pipes or the seal between the wall (tiles) and the edge of the pan.
You could check that by leaving it running for a while, ensuring that the walls do not get splashes and all the water falls into the pan.
If it leaks then, it's the drain pipes under the pan and they should be refitted or replaced.
If it doesn't leak under these conditions, then you have to see to the tile grouting and edge seal.
Either way, a competent plumber should easily be able to deal with this.