How to tell is phone is cloned from other device and being used by other individual

Just going on a hunch here, and wondering if someone else may be cloning my phone and able to see everything I am doing on my android and viewing private information, putting my accounts at risk and using accounts, deleting emails, watching for passwords, etc. Again this has been going on for sometime. I want to see proof and want to know WHO. I WOULD APPRECIATE ANY HELP AT ALL.

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