Sony Ericsson W8 — Touch problem

Address:

Bhopal, Madhya Pradesh

I have purchased sony ericsson w8(e16i) model on 05/11/2011. This phone is not working properly , i have given it to service centre two times and both times motherboard is changed from company but again the problem occurs..
please change my cellphone with new one or other one.
my mobile is in under warranty.
old imei no. is [protected]

second imei no. is [protected]

present imei no. is [protected]

sir if this problem will ocurred again and again what will i do after warranty..
please do some favor .
thankyou..
vikash singh..
email- [protected]@gmail.com