The TV can't be "hacked". As @Rich_T asked, please be more specific about what's going on.
Roku devices can be controlled via an app on a phone or tablet. But such device would have to be connected to the same network as the Roku. Perhaps what you're seeing is someone using the app to control your TV because they figured out your wireless password. Change your wireless password, then reboot your router to break any existing connections. Once it's back up, connect your wireless devices using the new password, and odds are the person messing with you will be locked out.
Dan Ultra (4640), Ultra (4670), Ultra (4800), Premiere (3920), Insignia 720p Roku TV, Sharp 4K Roku TV, Nvidia Shield, Windows 10 Pro x64 running Serviio and Plex on a wired Gigabit network.