Exchange without a receipt.

I Boutht 2 dresses for my Mom who is 76 and does not do her own shopping, from Truworths Heidelberg on the 29th of August. Both Items were to big for my mom. I thought the receipt was in the bag. I went today to exchange the dresses and we could not find the receipt. I was at the store where I purchased the dresses and told them the date of the purchase and I asked if they could re print my slip. They said they can't re print receipts and they refused to exchange the dresses. I am disgusted with the customer service in store. The Manager Lerato was very unsympathetic and just refused to exchange the dresses I am forced to sit with 2 dresses that cost R1500.00 and my mom will never be able to wear them. I am shocked at this service from such a big retail store. Most other stores would have helped me no problem. Please can somebody get back to me on this