Implement a better system or train your staff please

I am very disappointed with Truworths at Phokeng Mall, I went to there to exchange my children's clothes for bigger sizes, When I got to the store I realized I didn't have the receipt/ slip with me, I didn't know if I had forgotten it at home or lost it, I made them aware that I misplaced my receipt but they refused to assist me. I didn't use the account to purchase, but I used my debit card, even when I offered to tell them the exact date and time of the transaction they still refused to help me, I am now wondering, had I lost the till slip completely I'd be stuck with small clothes not being able to exchange? mind you I used transport to get there, I had to go back home to look for the receipt which I found in my other purse. I find this very unacceptable especially for the big store like Truworths, I don't know if it is lack of staff training or the system needs to change completely. I am very disappointed, I am not happy at all, having to take a taxi back home to look for the slip and another one back to the mall for something that can be done by other small shops is really upsetting. Move with times please.