I went to my cellphone provider and had them replace my SIM card. My phone behaved normally for a day or so then reverted. I eventually realized my ex had access to my online cellular provider account information and he had changed the password to it so I couldn’t make any changes online. After changing cell phone providers, changing all of my devices and email addresses, I finally rid myself of him. They can also hide apps on your device. I took my phone to the library and plugged it into the computer, typed “hidden” and was able to view all of the apps he’d downloaded to my phone. It does sound like your phone is hacked. The hacker has your imie, serial number, SIM card number, make and model of your phone so your best bet is to get a new device using a new Apple ID and strong password. Change all of your settings so that you aren’t even sharing information with developers. All developers are not good!

My ex did the same thing to me. I had to purchase new devices, change cellphone provider (he copied my SIM card and had online access to my specifications), and create new email addresses before I was completely rid of him. I further moved out of state and my address in not known to him. I closed my bank account and opened another, opting out of online banking. While having cellphone provider and bank account statements online is convenient, it is a nightmare after being hacked. As such I do not allow for access to sensitive information online anymore. I sincerely hope that your issue has been resolved and if not, I hope this helps you.