How to unroot my devices. PLEASE HELP???

[AC Question]

My devices have been hacked into... They got into it through Bluetooth and my Wi-Fi... I have master reseted them so many times and it's still here. They did something that when I restart the device, that's when and or how it got there. Like an overlay or something like that. I have tried almost everything to remove it and it is still there. I'm loosing hope... Someone please help???