Cash back paid to wrong bank

My fiance was expecting to get a cash payout from Old Mutual, and he was informed around January, then he then took a copy of bank statement to Atteridgeville Old Mutual to update his particulars. Then on the 14th March 2022 he went to the same branch to check for other things and inquire about the cash back, that when the guy who assisted him reqested a copy again, and he went and printed one from ABSA bank. The guy assisted him promptly, and he was told that the money will be in his bank in the next coming 5 working days, to our shock the money was paid same day but to a different bank being Standard Bank, which he believed to be closed more than 10 years ago. Now Standard bank has taken half of the money towards the monthly finance charges and Old Mutual says they wont be able to assist in that, and it is worrying that mistake has been made but who has to pay the difference that Standard bank took, because the active bank is ABSA and relevant documentation were provided twice.