Thats because apps represent greedy, lying, thieving corporations. I just went through the same thing with the find my phone app. I had it shut off only to have it turn itself on days later. Then I got several phone calls at midnight, with no one responding, attempting to turn it back on. Those phone numbers were from the lying real-estate company that's selling my place. What a great way for corporations to gather and sell your personal information.
Your phone has been infected with malware. Try to remember the last app you installed prior to this happening and uninstall it. Turn on App Protection in the security settings, run a scan and clean it up. You might also have to download a third-party malware scanner/cleaner. When things like this happen it is nearly always a user induced occurrence that happens by visiting a questionable website, clicking a bad link, or downloading sketchy programs.
