I need some advice. Anyone!?

Alright, I know this sounds weird but, I think my dad stole from me. He cosigned on a student loan for me of 12k. We agreed he would hold onto half of it until I really needed it. Ever since the agreement, my dad has never returned my phone calls. I am currently in a lease in his name and my financial aid is what I used to pay rent whenever I did not make enough in the month. I'm thinking of vacating the apartment because I can no longer afford it since my father wont return the money. It's been a few months since we spoke. I also planned on sending the other half back to the bank if I did leave the apartment, but how can I if he keeps it. This loan is on my credit and I have to begin paying it even though I never got the other half. What should I do?