Go to the Google play store and click on the button top right and then select Payments and Subscriptions, then Payment Methods and delete any, or all, of the payment methods. I do not have any set up so I cannot accidentally buy an app.
First thing to do is go back to where you bought the app and see if they have a returns procedure. If they don't try customer services on 333. Finally, and someone will say it, double check before you click buy. It is easy to get caught out unless you are careful. I had 4 books in my basket with World of Books and I clicked to pay and by the time I got back to confirm purchase they had put up the price of one book which doubled the price of my basket. Needless to say I emptied the basket and shopped elsewhere.
