DirectAxis refuses to give MY MONEY BACK WHICH I MISTAKELY TRANSFERRED TO THEM

I mistakely transferred money into the direct axis account instead of my fnb personal loan, because on my bank statement it shows both as a personal loan, it is not distinguished as direct axis or fnb personal loans, I have asked them to give me my money back and they are giving me the run around, now they want proof of payment and when I send them screenshots of the transfer made they want the proof of payment, I have already explained that is it not a payment made, its an inter transfer but they are insisting that I must give the proof of payment, they refuse to give back money that is mine, and making it very difficult for me to get my money back, I would not expect this from the first rand, to take money that belongs to me and not want to refund it, i dont know how to give them proof of payment other then a screen shot of the transfer because on my payment history does not show an inter account tranfer, now I must run around to FNB to help me get this just for money that is MINE, this is really pathetic I will never do business with them again and I am going to change banks altogether - THE TREATEMENT FROM THEM IS SO DISRESPECTFUL TREATING ME AS IF I AM LYING ABOUT THE MONEY I PAID TO THEM, accusing me of lying saying that I asked for their bank details, the money does not belong to you, refund it,