How do I prevent extra payment on in-app purchase

You should choose the option for email or chat. That is where the Apple people are. This site is a user-to-user forum so people here can not resolve your billing problem. Was there not a button for Visit iTunes Store Support after you pressed Report a Problem?

If you are having trouble with the iPhone links, try the Report a Problem link in this article. If you see 'itunes.com/bill' or an unfamiliar charge on your statement - Apple Support

Hi,

Your screenshot shows a Report a Problem button. Use that.

It should not have. Try again on all the disputed purchases.