Sony Ericsson K550i — display error

i m your cusotmer sony ericsson k550i i purchased this handset from one of your outlet satyam telecom(jayanti bazar jaipur rajasthan) in the month 07 july 2007, i m facing the problem about "WHITE SCREEN" and complained for the same 6 times in last 4 months at ur service center situated at jayanti bazar(jaipur rajasthan) they always kept this handset for more than 15 days and last time i submited this on 16the june 2008 and i received back this on 12the july 2008 with the final and sure commitment that now onwards i won't face the same problme but again same day i received the same problme with error msg:"inactive sim card" i m highly unhappy and dissatified with ur services pls concern my matter asap or i will take a legal action on the same...