OLD MUTUAL REFUSING TO PAY CASH BACK

I was due for cash back on one of my funeral policies and I was told it was paid into my Standard bank account. I waited for the money to reflect but it did not. I went to OM branch in Somerset West. To cut the long story short, I have been back and front from OM to SB and SB to OM. According to OM they have paid the money into my old account which has been closed since Feb 2018. Now they want me to get a statement from SB and I have been to SB and I was told there is not statement for a closed account. The account has been inactive for 19 months. OM is refusing to pay my money saying it is my responsibility to get a statement from SB. Now I do not know what to do. I gave Old Mutual the proof that that account they used is inactive. I do not know why would they go and put money into an inactive account, while they are having two of my active bank accounts; one active account from standard bank and one active account from CAPITEC. LOOKS LIKE I WILL NOT BE GETTING MY MONEY. In any case, I have had it with OLD MUTUAL.