customer made reservation 6pax in one room

I have a customer who did a reservation and not well made

I need some help

Anyway I am new but I didnt know that this would happens

They booked 1 room for 6 people! Not refundable also

Trying to contact them by phone but the phone number is wrong

I sent many emails but not reply

I contacted booking.com but not reply since few hours already 

I dont know what to do, shoud I give the money back?

I am afraid they will go to the place  today but there are already people in the mobilhome, not possible to put 6pax

Regards

Vanesa