iPhone 16 Pro Max No Signal and Warranty Repair Dispute

My iPhone 16 Pro Max suddenly lost its cellular signal while it was sitting on a table and I was not using it, and the signal has never returned since. The device has never been dropped, damaged, or even scratched, and it has never undergone any repairs. Due to this issue, I sent my phone to an authorized service center under warranty on 12 October. After inspecting the device, the service center emailed me stating that there had been “unauthorized intervention” and that the motherboard needed to be replaced at a cost of ₺54,000. I strongly reject this claim and the excessive repair charge, as I have never had any work performed on my phone anywhere. It is unacceptable for such an expensive device to develop a fault during normal use and for the responsibility to be placed on the customer without clear evidence. I request that my device be repaired free of charge under warranty or replaced with an equivalent defect-free device. Alternatively, I request an appropriate solution involving a refund or reimbursement. I also demand that the technical report and evidence supporting the allegation of “unauthorized intervention” be shared with me clearly and that my grievance be resolved as soon as possible.