destroyed bathroom

[Eszter25]

Hi Hosts!
We have a guest now, actually two because a guy booked our apartment for 9 nights for one person but he arrived with his girlfriend and they are staying there together. Today he sent me a picture of the bathroom's floor like its full of water and what can he do.We went to the flat with my father immadietly to fix the problem but we live far so it took time.

When the girl was taking shower (who wasn't there legally and I can't imagine what did she do in the shoewer in fact) her hair and body hair plugged the shower but she didn't take care about the lot of water what was in the tray. The water came out from the shower and swamped the whole bathroom's floor. When we arrived to the flat after one hour, they started to put celan sheets(?!) to dry the floor in turn there were rags in a bucket for cleaning. 
My father get the filter from the shower out and the water went down immediately. That was all what they'd had to do. We spent 3 hours there to dry the bathroom moreover the bathroom's furniture is tottaly wet and demaged from the water.
What do you think what should I do?
I told to them that they booked only for one person and it costs more when there are more people because of the taxes and everything. I sent an ask to the guy to edit his reservation for two people but he didn't do anything.
The shower was new but the demage is big (I don't know exactly how to count for them). Moreover the ceiling of the flat under us can be wet too. 

I have never had guests like they and problem like this. 
I wish better new year start for everyone!

Eszti from Hungary