unauthorised double debit my account

On the 18th December 2015 African bank debited my account R1383.99 and R500 and I called to query that - the 1st agent i spoke to, ensured me that the money will be paid back into my account within 24hours and clearly stated that I'm only getting paid on the 21st and the money they debited was from my overdraft, which made me bear interest costs. I called again and the 2nd agent told me that they not going to reverse the debit because they confirmed with my employer to confirm my payment date for December - I was not happy about that because that's my account and not my employer's account. On the 21st of December the debited my account again with the same amount R1386. 99 and R500 what the ... is going on here? You're busy debiting my account without my authority as you please and making me bear unnecessary costs. I want my money refunded and those interested charges paid. I need full explanation. Pay Back My Money - you have no respect.