N72
Invisible display-handset problem

Dear sir.

I have purchased n72 in universal cmh rd bangalore on 23/11 emi no. is 356966016001143 type RM 180 code 0548028 now Iam facing problem I have given 3times at tippasandra nokia care centre but they did not solve the problem simply they keep 5-8days and give it back stating it is ok now pls advice what to do and how to get my mobile repair or replace and how long i should wait