How to prevent unauthorized access and protect iCloud Photos after software update?

Last week updated software to my phone but I not believe bco I know after down load the software I see the screen of my phone update. Complete I suspect one of IT in operating to help and guide the subscribers who to make me a trouble and using my phone apple account for nude photos and video one day I notice the video but suddenly disappear. Even I using apple support I don’t understand why and what happened my request change password using key password after that I login again wrong password apple come. today want to go in apple bar to us question why and happened to my phone I using all apple application and apps on