Angry customer

Hey good afternoon my name ia mathapelo i made a laybye at ackermans waterfall mall yesterday dated 30/09/2018 only to realize when i got home that i took size 5 instead of 6 so today i send my sister to go change the shoes sizes to 6 they refused to help me saying tht i should pay for it cash in order for them to help me they are not able to go inside the office were the lay byes are kept if i want those sizes i should lay bye new ones please assist