Identify store disappointing

I bought winter pyjamas for my son on sale R290 on Sunday 6th 2023 at Identity Northgate mall. They were were a bit small so I wanted to change and get a bigger size today Monday only to be told I have to add R100 because the sale ended. I couldn't believe this since its exchange and its not even on their return policy. I even asked for the manager and she told me the same and even went further to say they are different from other shops. I was so disappointed and asked for my money back and not getting the pyjamas I wanted most.