How can someone take control of my account

[clairb...@gmail.com]

I set up an account for my step done for his Samsung tab 2, I put his name in there and put money on the google play, now somehow his mother has taken control of the account without my step and removed my recovery number and email address, and she didn't know the pass word, neither does he! How can this happen? He can no longer sign in to his tab and he doesn't know what his mother has changed the password to. She is just a static to have got one up on me