Bad customer service

I received a very bad customer service at Mr Price Canal Walk. I bought something there in April this year and when I was paying their faulty speed point switched off. I received a notification while still by the tills that transaction went through, but they told me it's not reflecting by them and I left without the item that I paid for. I've been calling them and going back and forth there to enquire about this but still this day I didn't receive my money back.My bank statement proves that transaction was processed by them but they tell me they never received the money. Management there is just pathetic and giving poor service.