Unauthorized deductions from bankaccount

I have never entered into any agreement with Getbucks, yet on 14-9-2018, they suddenly deduct an amount of R2 784.39 from my account. This was the only deduction. They now claim I owe them money? Unfortunately, I never picked up the deduction, yes I did not check my statement, otherwise I would have acted immediately.Wow, they don't show me any contract between us or where I have signed anything or in which account the 'supposedly loan money' was paid into! Who can help me?