cheating sales is going on with defective product in univercell as aadi offer

Location/place: madurai

Name of company/service: univercell

sir,
i went to madurai univercell shop near annanagar to buy a andriod mobile for a price around Rs.7000.I actually had a idea of buying samsung. They suggest me a byond b 63 model mobile and its cost is around 12000 and due to aadi offer they said that we are offering this for 6500. since its on my budget and it having more option and their words about the company made me to buy it.and as a buyer usually we choose a best offer and because of their shop name i accept their offer.But i found it defective on the next day on 20th july, they replaced me with a new one but i was not satifised with product name so asked them for replacing with some other company but they assured me.now today 12th august 2013 again i had a problem, it did not open at all.so took it again to the shop because it happened again within 20 days.i asked them to replace with a new one cause many online shopping promotes 30 days replacement as a seller policy,Actually we are buying a product from near by shops because of some guarntee that the shop we purchased is near by our town. but they replied me to took it to the service center.
1. actually why i have to took a new mobile to a service center,
2.did i planned this mobile to buy, they convinced me to buy even after the 1st replacement.
3.eventhough there are many onilne shopping offering more than this and with 30 days replacement, why i have to go with this.. what a hell… my purchase bill UTN number is 0894986, tis no -33670781737, CST no- 875295/28-09-05. place ( univercell, anna nagar, madurai, tamilnadu. )