HCL Tablet Problem

Location/place: delhi

Name of company/service: student

respected sir.
i purchased HCL tablet on 20/07/2012.after 3 days it is not working propely i give it to the service centre(TOUCH NOIDA SECTOR-15) .they correct it but after 5 days again its not working properly then again i put my tab in service centre(TOUCH NOIDA SECTOR-15) on 7/7/2012.they said that the SD card is not working so you come after 2-3 days,but after 9 days my problem is not rectify they are making many excuse and i am facing many problem in study.due to tablet,so please i want to know that why this problem occur.
Thanking you,