1800 down the drain help

Accidently deposited money into a wrong account holder and immediately alerted the bank customr service because already the bank was closed... And told they can't reverse the money without the customer agreeing 2 it and told they will contact the customer who's phone has been on voice mail ever since.. It looks like the customer doesn't even use that number anymore and has not changed their details with the bank... 1800 is a lot of money which is not even mine and owned needs it pls assist capitec, nobody can switch of their phone for so many days, is the account even active,