What do i do?

my ex and i had a joint bank account.we broke up and the account was negative.now,i found out that he got a loan from a site like prosper and it was deposited into our account then he took the money and closed it..now hes saying I got the loan in his name w/o his knowing(which i didnt).i didnt even know there was money in the account and I never used any of the loan he claims i got.he took it out and put it in a cd and turned it in to the fraud dept of the lender.what can i do? hes trying to get back at me for our relationship but i really had nothing to do with this.especially since i didnt take any of the money,i cant be blamed right?