Terrible Service

I bought shoes for my 2 years old who is a big boy. I bought a size 8 which is the correct size the problem is that his feet couldn't fit into the shoe. I misplaced the slip but the shoes are still in a good condition with the price tag still on. The shoes cost R149.95 and when I took them back to the store I get told that since I do not have the slip they will give me with the system price which is now R99. It didn't make sense to me because I was not asking for cash but simply exchanging them. The cashier's attitude was so terrible that I couldn't even say much and just took the shoes I had brought back. I didn't mind with what the cashier said but what really upsets me is how they said it. This happened at Ackermans in Diepkloof square and because of their terrible service I will never ever go back there!!!!