Question about parking in private car park spaces, resident flats?

Quick question, I live at a residential block of flats and we have an allocated parking space each in the rear car park. All clearly numbered. Since Christmas eve morning, someone has parked in my space. The car has not moved and I have tried every other flat to see who it belongs to. It's a nusiance and I am now having to park miles away which is a pain. My maintenance company are closed until January and I am out of ideas...... Any advice? Thanks.