refusal to exchange within a 7 day period

I purchased a charger from mtn store in menlyn. I opened the package the same day and it was working. The next day it didnt want to work anymore so i returned to the store. The same man who helped me before said he refuses to exchange or credit me without the charger being in its box while i have the receipt. I explained to him that i didnt keep the box because it was working at first and he did not inform me to keep the box incase it doesnt work. He called the manager on duty and i explained to her aswell that as a mtn customer why must i walk out with no charger after spending my money there and getting nothing for my money. I was very upset and im still disturbed by this experience i was in tears. I spent my money and my time only to be treated like i am ******* and not a valued customer. I told them to keep the charger and said i will report to hello peter and i walked out of the store. The service there is shockingly bad and as a person who also works in retail i know that this is unacceptable. I left the store without a charger and without my money and i feel done in.