First, what makes you think that its been hacked? Has someone had your phone for a some time to themselves? It requires turning on a certain setting in your phone, then downloading an app, opening and configuring. That's one way. Otherwise it's going to be one of your accounts that would be hacked, like your Google account. You can go to your Google account and look at logged in devices and or any suspicious activity. Google is pretty good at keeping tabs on that for you.