refusal of refund

I went to clicks at Hatfield plaza in Pretoria on the 28th of October 2022 and bought a bottle of shampoo, thereafter I went to pick n pay and found that same shampoo at a cheaper price so I bought it there instead, after my shopping at pick n pay I returned to clicks to return the shampoo seeing as I'd got it at a cheaper price. Unfortunately I had lost my till slip but you could clearly see the bottle was still sealed and management were even able to find proof of my payment on the system. The manager was extremely rude and had a bad attitude and refused to give me a refund and made me wait half an hour just to say I can't be refunded. I AM HIGHLY UPSET