Pathetic

So last Thursday DMC debited r4900 from bank account supposedly as an arrangement between them and my sister for her Capitec Loan account. Somehow my sister had my details and it seems she gave them the details over the phone to debit my account. Now my question is, should me as the account holder, give that voice confirmation to them to debit my account? After all the call is recorded as proof that i as the account holder gave them permission to debit my account to repay my sister’s debt? Also when giving account details over the phone, Is it possible to allow someone to give some else’s account details to be debited? How does DMC confirm that the account number being given is that of the account holder? I want my money back. This is the DMC ref number ********** 6.