Worst online shopping experience

I’m a regular customer of Mrp. I recently bought a shirt online and it was delivered to the store at St George’s mall Cape Town. I collected the parcel and took it home. Upon opening the parcel later that day I discovered I was sent a dress instead of a shirt and no slip was included in the package as well. I went to the store and explained what had happened but I got skeptical looks from the staff and nobody was sympathetic towards my situation. I was told they cannot exchange the dress I brought back for the shirt they had in stock at their store because I have no slip. I even showed them on my app what I had purchased but no luck. I used the WhatsApp line afterwards and sent pics of my order and what I received. I was told my complaint would be escalated and I would receive feedback via email. I still haven’t received anything. I feel like mrp is telling me I should just keep the dress that I don’t want and shut up.