iPhone is unresponsive after battery replacement

Hi,

My IPhone was 3 years old and the battery was beginning to become very unusable due to the battery life. I ended up replacing the battery myself with one I ordered off the internet. For the first month the phone worked fantastically.

Two days ago after my phone battery died whilst I wasn't at home the phone will no longer respond when plugged into a charger and after going to the apple store they simply said it no longer works and is unfixable. I didn't tell them the last month I replaced it myself of course. I was wondering if anyone has an answer to this?

I was about to just buy a new phone but could it just be something as simple as getting a new battery? If the problem even is the battery or is it something more serious.

Thanks!