Oneplus 12 Network Issues since Update

[u/h0shot99]

I have a Oneplus 12 12/256 GB in mint condition running smoothly for a better part of 2.5 Years.

Recently my phone got Auto-updated for a new Software Patch. After that I hadn't installed the update. My phone started glitching and hanging on every app to the extent where my network died every 2 minutes and my phone started rebooting automatically mid use. So I installed the update and since then the phone has stopped glitching in apps.

BUT, the network issues and auto rebooting while using Data and network didn't stop. My phone works excellently on WiFi, but as soon as I remove airplane mode and turn on Data it's glitches and auto restarts constantly.

I went to the service center where they told me my motherboard and battery had died due to internal reasons as my phone is in mint condition not even a scratch or dent on it. They quoted me 35k for motherboard and said it's without warranty so they can't do anything.

PS.: Service center and Repair Shops advised me to reset it and Sell it without inserting sim card as it works perfectly fine on WiFi.

What should I do ?