How Can I Resolve a Persistent Security Breach on My Devices Despite Multiple Measures?

I’ve been experiencing a severe security breach where individuals have hacked into both my Android and Linux devices. They have access to all my online and offline activities, including my social media accounts, Gmail, WhatsApp, call logs, and SMS. Despite resetting my phone multiple times and enabling two-factor authentication for all my accounts, I am still unable to remove these intruders. I’ve also used the paid version of Bitdefender for malware protection, but it hasn’t detected any malware. I am confident that the intruders remain in my system. To check if my phone is still compromised, I posted a story on Instagram and used the 'Close Friends' feature to share it only with my other account. However, I discovered that the intruders were still able to see the story. Additionally, they have made comments about my personal online activities that they should not have known about. What further steps can I take to ensure that my devices are fully secure, and how can I conclusively verify that the intruders are no longer accessing my information?