capitec want me to pay for theyre mistake

money was deposited into my bank account from my previous employer, i was not suprised because ive received money from them previously from back pay that they owed me, i withdrew some of it 2 days after ive received it, then a few days after i got a phonecall from capitec bank informing me that they made a mistake and deposited the money into the wrong account, i was suprised because it was from my previous employer so i wasnt sure how this mistake could be made anyways they took the balance that was stil in my account and requested that i pay back what i used, the problem is i didnt make the mistake im unemployed and wil not afford to pay a bank for the mistake that they made any advice would help please they are threatening to take the matter to court if i dont make payment, im so disapointed in this bank really they left me embaressed because i did not ***** the money .please help