Exchange at Mr Price Dobsonville is problem.

Am very dissatisfied and disappointed at Mr Price Dobsonville mall. I sent My wife to change one of the items that we bought yesterday at their store since am out of the area today. They are telling her that it is not possible to change without the owner of the card. Keep in mind that she has the item she is going to change and the slip and my account card for confirmation. She is not buying anything she is just exchanging from one size to another. So the store manager said to me that i need to leave whatever am doing and come to the store to exchange because am the card owner. I requested that if this is the exchange Sop or procedure they must show me where it is written down so that we know that it is not allow to send someone with the slip and the card to exchange because we know that we cant send some to buy with our card, thats *****.... we used money to go to the store just to be send back without a vaild reason..the manager said some things should not be written down. Please assist me with the correct exchange Sop or procedures because the manager failed to provide me with an explanation as to why can't my wife exchange one item of which it was bought yesterday at the very same store and she has came with proof. Am so disappointed at the manner the manager communicated with me over the phone call saying not everything must be written. I dont know if thats how Mr price treat their customers..