Samsung — to replace my sdhc card 8gb

respected sir! i bought a samsung sdhc memory card 8gb from home shop18. when i get this memory card i didn't open this. after 2 days i opened it and put in to my mobile phone it shows blank memory card. it shows nothing. i complaint about it at hs18 but they said it is not our problem you should say to samsung compny because memory card has 5 year guarantee. i contact to samsung company but they also said it is not our matter you should contact to hs18. sir i want to replace my sdhc memory card.