SONY XPERIA
No proper service and response

I purchased xperia-U by Oct since the first week of purchase i face issues with my phone performance.

Issue: Phone hangs quite often, restarts on its own, speaker/earphone goes off during call, display looks cracked when it hangs.

I have given my phone for repair for about 8 times in which mother board was replaced twice but for absolutely no use.

They just do software update claiming it would fix up the issue otherwise. The worst part is everytime service centre people hold my phone atleast for 10 days, and couple of times they held it for more than 3 weeks.

So the customer care senior people said they would replace my phone if it does not work in their last repair.

But now they again asking me to bear another repair and no response from service centre even after 15 days by now.

Already 5 months of my warranty period is gone, it seems like after another 6 months they would end up saying that my phone would never be repaired or replaced as i lost my warranty.

Why a customer should spend all 5 months running behind a service centre for problematic phone?