Exact Sanlam Plaza Bloemfontein

I bought the first item on the attached file of my receipt yesterday. It's military boots that I bought at your exact store in Loch logan bloemfontein using a voucher you guys sent me on the 24th of April with the following code PDYKAVUQOPII0E8. I purchased a size 11 and used the voucher at the Loch logan store to get the discount. Now the size is big and went to exchange it and Loch logan does not have a size 10. So I went to the branch in Sanlam Plaza to exchange. When I get to the till the lady tells me that I cannot exchange on the same amount of the voucher I now have to top up inorder for me to exchange the shoes. Now this buffels me because I was not told such when I purchased the shoes and I also won't be able to top up the amount for something that as a customer I was not told about. Now the guy who came to assist the lady on the till says there is nothing they can do, I either exchange the shoe and top up the amount to get the original amount otherwise they can't give me the size I'am looking for. When I asked for the manager of the store I was told that the person is not available and will only be available on Monday. Now I would like to know what must I do now woth a shoe size that my child cannot wear because it's big and you guys not wanting to exchange the size for me simply because I used a voucher that you guys gave me to use and now you guys want me to pop up more money for something that I was not even told about.

I sent them an email on Friday and they still have not gotten back to me.