Dear Korrakot,
This is Mohan from iTunes Store Customer Support.
Thank you for reply.
Korrakot, sorry for the inconvenience caused you after reviewing the circumstances of your case, we determined that issuing you a refund for your unintentional purchase of "35000เพชร" is an appropriate exception to the iTunes Store Terms and Conditions, which state that all sales are final. In seven to ten business days, a credit of 49.99 USD should be posted to the credit card that appears on the receipt for that purchase.
The iTunes Store provides a warning message that asks if you are sure that you want to buy an item. This warning can be turned off. If you would like to make sure that this warning is on, you can reset the warnings in the iTunes Store by following the instructions in this article:
Resetting iTunes Store warnings
http://support.apple.com/kb/HT1734
Additionally, you can make modifications on certain devices that will prevent them from making purchases:
iOS: Understanding Restrictions (Parental Controls)
http://support.apple.com/kb/HT4213
I hope the above information helps you. Your satisfaction is my priority and I will be happy to help you further.
Thanks for being an iTunes Store Customer.