Frustrated

On 24 May i went to Mr price at liberty promenade, purchased a few items and paid for it..unfortunately the system deducted double the amount and i was told that it will be reversed etc. Its been a week and still no joy for my refund. Im frustrated asthe manager at the store informed me that the money would reflect in my account on friday. I understand mistakes happen but this is the longest ive waited for a reversal!!!