Security
Recently my home was burglarized. The thieves stole an old iPhone. My old iPhone had my iCloud account on it as well as other information/passwords in the "Notes" app. I went to my local AT&T store and they said they could delete the data from my old iPhone. I can not recall if I still had "screen lock" active. Days after my old iPhone was stolen I have had issues with my IPhone 6S. Not only do my settings get changed (not by me) none of my apps will update to the new iCloud address. My iPhone 6s keeps asking for my old iCloud password. I went back to AT&T for help and was told by another associate that only Apple could help me with my delima. I feel like a crazy person from my setting constantly changing. I even have over 100 screen shots I've taken over the past month so I would Know, what I changed my setting to, to then find them changed back. I'm not sure the point of anyone knowing where I've "parked my car" in maps. I've even considered it's some type of "glitch". I've considered my iPhone 6s has a virus or hacked. AT&T told my a virus was very unlikely.
How can I determine what the problem is so that it can be remedied. I have all my apps turn off in "screen time" except when I want to use them then I go back into screen time, use what I need then go back into screen time and lock it. My iPhone 6s currently is a phone I can text with at its current state. I am not IT savey. Please advise in laymen terms for an older person. Thank you kindly.
iPhone 6s