Oppo — Refused replacement or service within warranty

I bought an oppo reno 4 pro phone on 4th of august 2020. Yesterday night i started experiencing unusual heating issues in my phone so i switched off the phone post which it cooled down. I turned it back on and it was on the whole night. This morning when i woke up my phone was switched off so i thought charhe might have finished. The moment i put my phone on charging it made a loud noise as if something burst and phone fell down from the table. When i took it to customer care, they are refusing to address my concern and are claiming that i have tampered with the phone. Despite my telling them that the phone is damaged because of the blast that happened. Can somebody please tell me why will i tamper with my premium phone which is in warranty and create trouble for myself?? In fact in the name of checking my phone, the service centre ppl themselves chipped off the color of the back of the phone and now they are claiming that motherboard needs to be replaced and are asking for rs. 16000 additional charges. Instead of addressing my concern, they are simply interested in money laundering. Please find all the evidence attached.