1. make sure that you have downloaded the wallet from a trusted place like their official website and not from a third party link because those can be fake.
2. check what your balance is in the wallet app, it might just be that the wallet gave you a new address after you used the first.
3. contact the unobtanium developers (or the wallet developers) and ask for help after you did 1&2
EDIT: here is their announcement topic:
https://bitcointalk.org/index.php?topic=527500.0