Unauthorized purchases

I just got my bank ledger with $269.77 in game charges. Last month I had charges & talked to my bank. They said since it was my debit card they couldn't back charge. I wasn't sure that my great grandson hadn't used my card. He said he didn't. I kept my card on me at all times since then but this month was outrageous. I'll stop my card but these charges have been made since my card renewal. If there is any way you can stop this I would appreciate it. Thanks Linda Brammer    P.S My whole family play Google games. Thumbs up. :^)