@lele6136 , Lisa, Sorry to here your device is letting you down. It does seam the Fitbit products have their fair share of problems from the forums I have read through. I guess what I would probably do is contact Fitbit one more time at the link below, ask to speak to a resolutions specialist, to see if they can make good on the watch(talk nicely), have your info./details/ammunition all ready to present your case.
If you do not get any where, may be time to stop buying their products or at least wait till product has been out a year or more and read the reviews before purchasing. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
http://help.fitbit.com/?cu=1