iPhone 5s shows charging but wont charge

My 3 month old iPhone 5s does this once in ten days. When the charger is plugged in, it shows the charging sign. But the percentage does not increase and the battery eventually gets drained. After that it shows the below screen. I have tried charging the phone after that continuously for more than a day and no luck. Instead forge the phone for a day or a two, and plug in the charger - it comes up with the apple logo. And behaves a good boy for a week before the issue resurfaces again. Tried all tweaks i found on the internet and no luck. It does not boot up in safe mode as well.

I took it to the istore. They tried flashing it, checking the battery performance. Everything was reported perfect. After a day with them it would be back to normal and they return it saying the issue is fixed. They sounded helpless. Though i managed to show them the issue live when it did not charge and showed charging. it has been three times i have given the phone to the istore and got it back in the same condition.

Am i the only person who faces the issue out of all the lucky iphone owners? 😟

Should i demand for a replacement? I'm facing this issue since the first week i started using the phone. The inconsistent behavior irks more as the istore guys says they will not be able to claim a replacement. Request some serious help in this. I dont think i can live with it. 😟😟

I believe this forum is noticed by the Apple technicicians\officials. Any help on this would be much appreciated!!

Thanks!

Cheers!

Srihari