Unfair conduct

I bought a sensor for my car at goldwagen near Carnival mall and the sensor was incorrect with I had swiped with my bank card, so it happened I misplaced the receipt but I had proof of payment on my bank statement, I therefore returned the sensor for a refund,producing the bank notification to prove that I had purchased the sensor at the particular branch but the refused to refund my money insisting that If I don't have the receipt they won't refund my money, which I found unfair because my bank notification sms everything to prove that I bought the part at their shop, now I'm left with a sensor wich is not for my car