Disgusting attitude, terrifying experience.

Yesterday on 29-09-2017, I went to Game store in Woodlands to exchange my watch which had a fault. Before I went to the store I had realized that I have lost my slip. When I got to the store I explained my situation to the first lady at the till whom told me that I should go to customer service. When I got to customer service and explain my situation to that lady she was immediately rude to me. She told me that she won't help me because I don't have the slip. I then told her that I bought the watch at that exact store on 02-09-2017 at 15:15 and had used a gift card to purchase the watch and had that gift voucher with me, so they can check that on the system as proof of purchase from that exact store. She then led me to the information desk to which I explained my situation again to the white man there and I don't know if he was the manager or not but, he was rude too. He told me that it's not his responsibility to keep slips. How does any person in customer service tell a customer that. He told me that because I don't have a slip I have to pay the difference. What difference I don't know. After a huge fight and argument, even had to show them the email I got from omnico( supplier of the watch), is when my watch was replaced. Worst experience ever in my life in any store.