No refund for wrong deduction from MiWay

Even though I have informed MiWay in time to change my debit order date, the money was still deducted from my bank account on the wrong date. After sending them the required documents regarding the deduction and being promised that the money will be paid back into my account within 3 working day the money is still not paid back. Upon phoning them the consultant told me that the money was reversed and the problem lies with my bank. I phoned my bank and according to them the problem is MiWay that needs to pay back the money.