No one will help me get my money

On 21 August I paid for fuel and oil at my local garage amounting to R645. On 28 August this transaction was completed when the money was deducted from my account. The problem is that the money is still laying in the unauthorized amounts and has therefore been deducted twice. The garage refuses to refund me as they only received one amount and say it's not their problem. I am not sure what to do and really need that money. Please help!