Hacked Iphone 6S

How could I find out if my phone has been hacked? My elderly aunt swore someone was in her phone for months I didn’t believe her because she could never show any of us proof none of her bank accounts were ever messed with etc well I logged into our WiFi which I never did before I always used mobile data and this person made it known to me he existed but it really scared me and I took meds I really don't take for my anxiety and I do not remember much except him showing me how he could easily shut off our alarm in our house and he had a pic of me and him. He told me flat out it was photoshopped. Long story short I sold the S8 I had, bought my first Iphone because I heard they are more secure, changed my wifi password. Months have passed well my son set up my Iphone for me initially after that I didn't use it until the other day because I got a notification that my cloud was not backing up and I needed to connect to a wifi to backup. So I did, since that night odd things have started happening an app was installed that i didn't install, my phone acts like it has a mind of its own, its a lot slower at times, sometimes it will say I do not have any mobile data then all the sudden work again, my talk to text doesn't really work at all anymore. I also got a message that my name, email and other info was found on the dark web. I just want to know if there is a way to see if they have compromised this phone and how I can get them out if they did. Thanks!!