Bad service/ terrible device aftercare

I went to the Centurion Truworths to have a cellphone I purchased in November sent back for warranty as it works intermittently. The ladies there were talking amongst each other and not helping. I advised them I do not have the warranty receipt(lost in a house fire). They did not care but insisted they cannot assist without it. What’s the point of the store having a copy when I purchase the device. The ladies there are rude and don’t have customer service. How is it my fault I was sold a defective device to begin with.