Not wanting to Exchange product bought last week

Good day<br> <br> I'm laying a complaint for Shoprite sales manager Renny Mafa at the Shoprite in Mfuleni, i was returning a product that I bought still in a package that was opened but managed to seal the package with sellotape, I bought the product last week and the product did not fit it was mot the right size, I lost my slip so I was returning it not wanting my money back just want to exchange it for the correct size, the manager tells me that they won't take it back because i had opened the product.<br> It is within my right to bring something back if i am not happy with it and it hasn't been used.<br> Product code: ***<br> It is really not about the money it is about what is right and wrong<br>