help! has my phone been hacked? what do i do?

(time is different as i was putting it forward while playing a game)

I wasn't using my phone when it happened. It started playing alert messages, the find my iPhones ones that are supposed to play when you want your missing phone to play a sound. I ignored it at first, just thought it was nothing and that it would go away, and then I got that message on my screen. Immediately i turned the phone off, went straight on the computer and reset my apple ID password. I then turned the phone back on and put it on airplane mode. Nothing has happened since. I was thinking of restoring the phone to factory settings, will this be sufficient?? As far as I know it is not jailbroken, it was a gift from my dad who lives in Qatar and he got it from the apple store in Doha i'm assuming. I have not downloaded anything or done anything I know of that would have been damaging to the phone.