Bad customer service

Last week I bought a 8gig memory stick at pep cell. It was the store manager who serviced me on that day. When I arrived at work to use the stick it was 4gig stick inside. hence that I was far I had to buy another stick elsewhere and I was on leave. After three days I went back to them with the stick, the cover, the receipt. The manager gave me a bad attitude and said she wont help me because she cant pay for stick. She just left me there on a counter as if I was an unwanted stupid *****. She said the stick was fine when I left the shop and she said maybe somebody could have change it. the question was how did she check if it was right because it was in the box or container.<br> Was very disappointed to be embarrassed like that in front of other customers, all what I was looking for was the apology and proper explanation if the items was not changeable<br>