Terrible attitude

I went to the store this morning. I had 1 item to return and needed to purchase 7 items. I told Nnana to add the difference on my account. She then said this would not be possible as I did not have the receipt for the item I returned. So I then told her please cancel the transaction I would not b returning the 1 item I would only want to purchase the new items. She looked so upset wit me. She turned to the computer and clicked her tongue and called for the manager to override the transaction. She did not look at me nor interact with the entire time. I then said to her I know that you are upset as you have to do this again but you should let customers know in advance that if they are returning an item and if they do not have a receipt for the item then they cannot add new items on and bill this to their account. She then looked even more upset even when she gave me the receipt she did not say thank u or bye (that's what normal customer service people do). Her attitude was shocking. She should not b working in customer service and the weird thing is that I dealt with her previously and also received rude treatment.