denied refund for a returned battery

builders Warehouse kempton park, I had a very bad experience. I bought a a unicross battery G/motor lithium 12V7AH, which I paid cash with my debit card, since I thought my battery was dead, only to find out my original battery is still working, it was wiring faulty which was fixed, so there was no need for me to keep the new battery and I returned it and they refused to refund me, it is complete, and within warranty period. they saying the packaging is not in original state of which is not practical, cause I opened it, there was no way it was going to be in its original state. I am a customer and I felt my rights where violeted by this warehouse.