Yesterday when I had the battery replaced at the Apple store, one step is they have to turn off the Find my Phone feature for some reason. That means, enter the password, and log out of the Apple ID. No big deal. I go to pick it up and we leave. To get the phone back to "normal" and to log back into Apple ID, enter the password. It keeps wanting me to log into an old ID that I used to have at my old email address. I don't have that one anymore and the there is no password, it is a dead account. So I go round and round with the phone and end up changing the password three times, but it want to use the old ID.
I finally called Apple Support. It is tricky, and totally not intuitive. They have a way of running a program on my phone to see the display on their end. She could point the places and click and enter the information. It was creepy to see my phone have a red arrow moving around showing what to do. In the end, it is all better now.