Refusing to exchange item

Good day, We were gifted with a Winfun 3 in 1 bouncer. We opened it to assemble it and there were two of the same parts (instead of being opposite parts). My Husband phoned Toys R Us Boksburg and spoke to Margaret who said we must please bring it in so she can see if they have stock. Which we did on Saturday. Margaret said we must please give her time to see if other stores had stock of same. Margaret called me this morning saying that the ones available are display models. She said she had spoken to her manager and said manager said we can bring it in to eith exchange for something else or a voucher. My Husband did just that. Margaret was assisting him and at the till said manager refused to do exchange saying it's a Baby city code on box and we don't have receipt. Firstly, I had phoned Baby city and it's not their stock. Secondly, Margaret was aware of no receipt and was very helpful on her part in assisting us. This product will surely go back to supplier??? Why not exchange as mentioned??? This needs to be sorted out. I'm sitting with a brand new item that cannot be used!!!!