How to know if your iPhone has been cloned

My device was handled by the person suspected of hacking. Stalker boyfriend claiming the “ I just care” thing. I have issues with the person, almost like, knowing things before I even tell them. It’s almost as if they can see my phone screen. They know everything I do on my phone and they don’t even need be around. It’s pretty scary. I’ve recently been overwhelmed with numbers calling my cell from EVERYWHERE both in the US and outside it. I was browsing through settings recently to try and detect anything suspicious and noticed how much space is being taken up by system services all of a sudden. I went from having 9 or GB of available space to maybe 1GB (with no recent major downloads) what do I do?

iPhone 6S+

Did you let someone physically handle your device while it was unlocked? What issues are you having that make you think it is hacked or cloned?