Welcome to Android Central forums. While my community mates have offered practical advice, I have questions.
Why do you believe someone is controlling your phone? Please give an example of what you are seeing?
Has anyone had unfettered access to your device, where it is unlocked and out of your sight for more than hour?
Have you installed any app like a Family app or parental control app, that someone else is the admin of the account?
Without the answers to the questions asked, just let me say, and maybe this will put your mind at ease some, maybe not, but people remotely hacking a device without touching it, cloning it to duplicate its contents and all of that spy stuff is just fiction. Even if they had managed to gain access to the device, they are not going to be able to control it remotely and send messages, or open certain apps as if they were on the device doing all of this. That is only possible for us regular people through Hollywood Magic and not real life.
Let us know what you find and give us a description of what you are seeing to think these things, more detail the better, and we'll provide the best advice we can.