Very rude and unhelpful staff

I went to pep in Elgin mall today (28 May 2019). I wanted to refund items that were bought for my gran which do not fit her. The items were now on sale I paid the normal price but I lost my slip . One of the friendly ladies changed the price to what I paid and advised her colleague on how to do so. She then rang up the second item and it was also now a reduced price and now they made me wait for 20 minutes while they tried to get a hold of meadow dale PEP where I had originally bought the goods. They were unable to get a hold of them and they refused to give me a refund and all I wanted to do was exchange it for something else, I didn’t even want the money. The lady that rudely helped me told me I must go back to where I bought it. I am very unsatisfied and my time was wasted because I am still stuck with items I am unable to use. I will never buy from PEP stores again if this is how they treat their customers.