Don't buy earphones from Vodacom

Bought earphones from Vodacom shop on Saturday in Beacon Bay Retail Park East London, the earphones stopped working by Sunday night the following day and when I went to return them for an exchange on Tuesday I was told that I need to have the plastic they came in also... They refused to exchange the earphones just because of a small plastic the earphones came in which of cause they never said I should keep when they told me that I could exchange them if they turned out to be faulty..... Also how do you sell earphones that have a life span of a few hours?