The leasing office says the appartmnent I booked is now unavailable..?

The apartment you were planning to move into is no longer available. Yes it is inconvenient, however the property management company does not owe you any compensation. There is no law that is going to make things work in your favor. You can either opt for another apartment in the community or take your deposit and fees and start looking for a new apartment. You are not entitled to compensation just because the current tenant decided they do not want to move.