If Apple "tier 3 engineers" cannot resolve this then it is unlikely the people on this forum (who are everyday users like yourself) can.
Unless you are somebody in whom a hacker thinks it is worth investing a huge amount of money in compromising your hardware itself, it is more likely that any compromising is to your account , not the hardware.
Read this document if you think your Apple Account has been compromised. --> If you think your Apple Account has been compromised - Apple Support
For iOS 16 or later see how Safety Check on iPhone works to keep you safe. Safety Check for an iPhone with iOS 16 or later - Apple Support
Use the information in this document to check your Apple ID device list to find where you're signed in --> Check your Apple Account device list to find where you’re signed in - Apple Support
Related materials:
Personal Safety User Guide
Personal Safety User Guide - Apple Support
> open the Table of Contents and review the articles
A document with general information about security and your Apple ID --> Security and your Apple Account - Apple Support
Contact Apple for help with Apple ID account security. This page provides country-specific Apple Support contact information ➞ Contact Apple Support - Apple Support