Billed to my credit card

I downloaded some FREE games on my new tablet.  I have now been billed over $150 from April 20, 2018-May 13, 2018. The charges vary from $0.99 to $24.99 on 10 different dates.  I don't understand how I am being charged for a FREE game.  When I look up an 'order' history on the site it says the charge is for a free game.  Can you help me with this?  I have stopped using my device until this situation is rectified.

Thank you!