Motorola Slvr L9 — phone not working properly

i am an existing customer of motorola slvr L9. i purchased this phone on 7th december, 2008. it started giving problems in the very first week like hanging problems & giving errors. i had to send it to the service center in january, 2009 (in just 1 month?) coz it simpley turned off & would not turn on. The service centre officials said it was a hanging problem & that now it would work properly. then after 1& a half weeks, the same problem occured again. it was sent to service center & we asked those people to kindly my handset as it's not possible to submit it again & again in today's traffic. but they simply refused saying it can't be replaced & that they would repair it again. Now. it's been just 1 week since it's back from the service center & it's turned off again. i request the concerned authorities to kindly look into this matter & advise wat do i do. i'm fed up of theis excuses & they are simply not ready to replace it. Please help.