No service supp****

I bought two of the same item, one in black and one in white. I tried on the black one to get my size and just bought the same size white one. When i got back in Robertson, i saw the white one is about two sizes bigger than the black one. I phoned a day and half later to find out if there is smaller items available. Two sales people would not assist me, one blatantly telling me there is no stock left over, even though when i was there day and half earlier, there was over 10 of the white ones left. I ask various times for help but they clearly and blatantly tried to misunderstand me and **** to me. When i returned three days later, there still was 6 items left, but only in the bigger sizes. The manager on duty told me to email a complaint to their customer services, but they refuse to alterate the top, since it was on sale. They refuse to acknowledge the fact that this problem is their own creation due to poor service and they will not let me speak to a manager other than the one in store, whom is not able to assist me other than apologise. Please help!!!