They are not depositing my money back.

Hello. I received a complaint for. Fnb claiming I had received a fradulent payment. I provided them with the reason for the payment and also a proof of payment to confirm it. My account was put on hold for a period of 30days. Saying they are still investigating. After that they asked for my other account such that they can transfer the money but they are not doing it. It's now more than 4 months . I gave them my other account confirmation letter but nothing is happening. Last time they called and gave me 72 hours. This is the 3rd week. Please help me out.