Terrible service

I bought this phone on the 19 Aug 26 and it was delivered on the 24, when i get home around 8pm, i opened the phone to start setting it up. I put the phone on charge so i don't run out of battery when setting it up. While the phone was on charge i heard a crackling sound from the phone, when i inspecting it i was a crack on the back cover and it was swollen, i then removed the phone from the charger as it as not and i was not sure what was happening. That's the reason i logged a claim with you. On the 25th Aug, i received an email saying that my claim was rejected, i haven't even used the phone and now i must pay for something faulty. This should be treated as an out of box failure. I'm not happy with the response, I didn't drop the phone. The phone got damaged whilst being charge and that should be issue from the supplier. If I didn't remove the from charger I could have suffered an injury due to a battery exploding, I didn't even use the device.