How did someone access my account

[AC Question]

My child took my phone to visitation with the other parent. When he came home, I could not open my phone via my fingerprint, it wanted a PIN, which I didn't set up. I went to phone Drs and they did a factory reset. I cannot see any texts. (Most stuff is in the cloud). My deleted emails folder is empty. I know someone hacked my phone and I need to be able to prove it. How?

 

[B. Diddy]

Welcome to Android Central! Which phone?

The odd thing is that you can't set up a fingerprint unlock without selecting a backup PIN or password, because sensors can fail. So you must have selected a PIN at some point

If these phone doctors did a factory reset, when you set the phone up again, did you have to enter the Google username and password that was previously on the phone? Were you able to get through the Setup Wizard normally?